Graph Tutorial

1. Introduction
2. The Components of a Graph
	Attributes:	xs
2a. Traces and Trace Sets
	Attributes:	linecolor (*)
			linestyle (*)
			linewidth (*)
2b. Title
	Attributes:	title
2c. Subtitle
	Attributes:	subtitle
2d. Footnote
	Attributes:	footnote
2e. Legend
	Attributes:	legend		
			legend (*)	
2f. x-Axis and y-Axis Titles
	Attributes:	x/X/y/Ytitle (**)	
			x/X/y/Ytitlefg (**)	
			x/X/y/Ytitlefont (**)
			x/X/y/Ytitlejustify (**)
			y/Ytitlestyle (**)	
2g. Axes
	Attributes:	axis
			x/X/y/Yfg (**)
                        y/Ymode (**)
2g1. Axis Ticks
	Attributes:	x/X/y/Yinc (**)
			x/X/y/Ymajorticksize (**)
			x/X/y/Yminorticks (**)
			x/X/y/Yminorticksize (**)	
			x/X/y/Ytickstyle (**)
2g2. Axis Labels
	Attributes:	x/X/y/Ylabelfont (**)
			x/X/y/Ylabeljustify (**)
			x/X/y/Ylabelout (**)
			x/Xsublabel (**)
			x/Xsublabeljustify (**)
2g3. Controlling Tick Mark Location and Label Formatting
	Attributes:	x/X/y/Ylabel (**)  	
			x/y/X/Yextent (**)
			x/y/X/Ylabelheight (**)
			x/X/y/Ylabelwidth (**)
			x/Xsublabelout (**)
2h. Alternate Axes
	Attributes:	axis
			x/yaxis (*,**)
2i. Zero Axes
	Attributes:	zero
3. Trace Styles	
	Attributes:	barwidth
			fillcolor (*)
			gradient (*)
			style (*)
			symbol (*)
			symbolsize (*)
3a. Text Traces
	Attributes:	title (*)			
			titlefg (*)			
			titlefont (*)			
4. Graph Attributes
	Attributes:	bg
			y/Ybottom (**)
			y/Ytop (**)
			x/Xleft	(**)
			x/Xright (**)
			x/Xmin (**)
			x/Xmax (**)
			y/Ymin (**)
			y/Ymax (**)
5. User Interactions
5a. Zooming
5b. Vertical Cursor and Cross Hairs
	Attributes:	legendstyle
5c. Referencing a Graph, Line Trace, or Trace Point
	Attributes:	coordinate/Coordinate	
5d. Selecting the Legend or a Text Trace
5e. Repositioning the Legend and Traces
5f. Copying and Deleting Traces
	Attributes:	delete	
5g. Editing and Creating Text Traces 
	Attributes:	addtexttrace
			delete (as callback function)
5h. Modifying and Creating Numeric Traces
	Attributes:	addtrace
			movelimit (*)
			selected (*)
6. Monitoring Performance
        Variable:       s.QUIET

(*) Trace set attributes, or trace attributes for short. All the others
are graph attributes.

(**) An attribute with x/X/y/Y prefixed to its name is one that is
separately defined for all four axes. The four axes are: the normal
x-axis at the bottom of the graph, referred to as "x"; the normal y-axis
at the left of the graph, referred to as "y"; the alternate x-axis at
the top of the graph, referred to as "X"; and the alternate y-axis at
the right of the graph, referred to as "Y". For example, x/X/y/Ytitle
means there are four attributes: xtitle, Xtitle, ytitle, and Ytitle, one
for each of the axes; x/yaxis means there are two attributes, xaxis and

1. Introduction

The purpose of this tutorial is to familiarize the reader with the graph
display class in the A+ screen management system. In general, only those
aspects of screen management specific to graphs are discussed here. See
the general screen management tutorial to learn how the more widely
applicable functions apply to graphs.

The tutorial is made up of descriptions and A+ examples. You should set
up your Emacs environment to have two visible buffers, one holding the
tutorial and the other an A+ session. If you are currently reading this
in Emacs, simply press F4.

To bring individual expressions from the tutorial into the A+ session,
place the cursor on the expression and press F2. It is assumed that the
expressions and functions are brought into the A+ session when you first
encounter them.

If you need more help on running Emacs and A+ see the "Getting Started"

Once you have an active A+ session, load the screen management system by

	$load s 

That is, place the cursor on the above expression and press F2.

At various points in the exercises, you will refresh the A+ session by
exiting with $off, pressing F4 to start A+ again, and then loading the
screen management system. Session refreshings will be indicated as
	$off  Exit from A+ 

Press F4 to start A+ again, then move the cursor back to the tutorial
buffer, on the next line.

	$load s

You may make mistakes when running the tutorial and it may become
difficult to get back to a place where you can continue. At that point
you should simply go back to the latest session refresh sequence and
start over from there.

Two more things before we start. First of all, by default graphs appear
in the upper left corner of the screen. To avoid having the graphs
overlay the tutorial, move the Emacs screen to the lower right, or put
the tutorial in the bottom Emacs buffer and the A+ session in the top
(you can do this by pressing F5 and then F6; you may have to do it more
than once.)

Secondly, even though the default sizes of the examples may be quite
small, don't resize them unless told to do so, because the resizing may
change the details of the graphs.

In the examples we usually display the graphs first and then set their
attributes so that you can see the effects. In practice, however, you
set the attributes before displaying the graph.

2. The Components of a Graph

A graph is a layout composed of one or more trace sets. The simplest
trace set is a vector v, whose elements are plotted as the y-coordinates
with x-coordinates #v. That is, the points (i,v[i]) are plotted for all
i from 0 to (#v)-1.

	v 53 14 27 2 31 85 30 11 67 50
	show `g is `graph

At this point you should see a window with "A+" in the grey title bar,
and a gray graph area below it. The graph area has a title area with "g"
in it, an x-axis and a y-axis, a legend, and a trace. This is the
default appearance of the graph. Each of these components can be
modified by setting the appropriate attributes, and there are other
components that do not appear in the default. And, of course, there can
be more than one trace on a graph. We will look at all of these
components in this section.

There are two attributes that allow us to control the size of the graph.
We will use these attributes for resizing to ensure that the assumptions
about the appearance of the graphs are correct.

	`g has (`xs`ys;(300;200))      This may have no effect, i.e.,
				       this may be the default size.

2a. Traces and Trace Sets 

The present graph g has only one trace set, i.e., one component variable
v.  However, like any container, it can have more than one. For example,


You should now see two traces on the graph, and an updated legend.

The more general form of a trace set is a matrix rather then a vector,
because then the x-coordinates as well as the y-coordinates can be
specified.  The individual coordinates are arranged as rows of the
matrix, with the x-coordinates along the first column and y-coordinates
along the second.  For example,

	x4 28 10 4 24 1 5 6 60
  8 10        	
  4 24		
  1  5        	
  6 60        	

You should now see three traces on the graph, and an updated legend.
Note that the new trace is indicated in the legend by "x:0", instead of
simply "x".  The reason for this is that matrix trace sets can provide
more than one trace on the graph. For example, if we catenate a new
column onto x as follows:

	xx(,@1 0) 40 20 50 80

you will see a fourth trace and a new row in the legend, indicated by
"x:1".  The 3-column matrix x provides two traces to the graph, both
with the same x-coordinates. One trace is defined by columns 0 and 1 of
x (the one indicated by "x:0" in the legend), and the other is defined
by columns 0 and 2 (and indicated by "x:1" in the legend). All traces in
a trace set share the same x-coordinates, which are in column 0 of the

Note that in the default case, the traces in a trace set share the same
color, but are distinguished by their line styles. Both line color and
line style are trace set attributes that can be set. For example:

	`w has (`linecolor;`yellow)
	`w has (`linestyle;`dot)
A full list of colors can be found in the A+ reference manual.  The line
styles are `solid, `dash (e.g., the trace indicated by "x:1" in the
legend), `dot and `dotdash. For example:

	`w has (`linestyle;`dotdash)

(Toggle back and forth between the last two expressions to see the
difference in the two line styles.) Also, `dot1 through `dot5 give
various intervals between dots, with `dot1 the smallest, `dot5 the
largest, and `dot3 the same as `dot.

	`w has (`linestyle;`dot1)
	`w has (`linestyle;`dot2)
	`w has (`linestyle;`dot3)
	`w has (`linestyle;`dot4)
	`w has (`linestyle;`dot5)

Analogously, there are `dash1 through `dash5 (different length dashes)
and `dotdash1 through `dotdash5.

The line colors and line styles can be set individually for all traces
in a trace set by specifying these attributes to have vectors of values.

	`x has (`linecolor;`white `dodgerblue)
	`x has (`linestyle;`dot `solid)

The last attribute affecting the appearance of line graphs allows the
line width to specified, which is useful for emphasis:

	`v has (`linewidth;2)

Note that the width of the corresponding line segment in the legend also
changed. The units of line width are pixels.

The last thing to be illustrated in this section is that a trace set
with multiple visible traces behaves differently in a graph with a
single trace set and in a graph with multiple visible trace sets. We
will use a separate graph and locate it 350 pixels to the right, for
simultaneous viewing. First, return the original graph to its default

        `x has (`linecolor;; `linestyle;); `v has (`linewidth;);
	xx4 28 10 4 24 1 5 6 60
	show `gg is `graph; `gg has (`x;350);
     	xxxx(,@1 0) 40 20 50 80
The two traces contributed by x to the graph g, which is a graph with
multiple trace sets, have the same color, but different line styles;
color is used to differentiate among trace sets. On the other hand, the
two traces contributed by xx to the graph gg, which has only one trace
set, have different colors, but the same line style.

	free `gg

Most of the attributes set so far have been on the trace sets, but three
(the size parameters `xs and `ys and the horizontal position parameter
`x) have been on the graph itself. This distinction is sometimes made
explicit by our referring to attributes as "trace attributes" or "graph

There are other visual forms a trace can take besides these various line
styles; see "3. Trace Styles."

2b. Title

The "g" that appears at the top of the gray plot area in our current
example is the title of the graph.  A more meaningful title can be
specified using the `title attribute:

	`g has (`title;"Graph Tutorial Example")

Both color and the font can also be set, and the title can be justified.
There may be a delay in changing the font. Wait for the change before
proceeding. (A list of recommended fonts can be found in the A+
Reference Manual.)

	`g has (`titlefg;`yellow)
	`g has (`titlefont;"helvetica-bold-20")
	`g has (`titlejustify;`left)                  or `right
	`g has (`titlejustify;`center)

The title can have more than one line:

	`g has (`title;("Graph Tutorial Example";"Components of a Graph"))

Note that the plot area composed of the axes and traces was
automatically resized to accommodate the two rows of the title.

The title can be removed by setting it to the empty vector:

	`g has (`title;"")

2c. Subtitle

One graph component that does not appear in the default form of a graph
is the subtitle. The subtitle appears between the title and the plot
area. Since it has color and font settings separate from those for the
title, it can be used for more effective title presentations. For
example, put the first row of the title back:

	`g has (`title;"Graph Tutorial Example")

and put the second row back as the subtitle:

	`g has (`subtitle;"Components of a Graph")
	`g has (`subtitlefg;`blue)
	`g has (`subtitlefont;"Times-Roman-15")
	`g has (`subtitlejustify;`left)               or `right
	`g has (`subtitlejustify;`center)

Subtitles, like titles, can have more than one row, and are removed by
setting their value to "".

2d. Footnote

The footnote is another component that does not appear in the default 
form of a graph. 

	`g has (`footnote;"Morgan Stanley Co.")
	`g has (`footnotefg;`yellow)
        `g has (`footnotefont;"Times-BoldItalic-15")
	`g has (`footnotejustify;`center)                  or `right
	`g has (`footnotejustify;`left)

Footnotes are removed by setting their value to "".

2e. Legend

The text in the legend can be set for each trace set:

	`v has (`legend;"solid red")
        `w has (`legend;"broken yellow")
	`x has (`legend;("solid blue";"broken blue"))

Note that if the text for a legend entry is the empty character vector,
that entry is removed.

	`v has (`legend;"")
	`v has (`legend;"solid red")

At this point you may want to resize the graph window, since otherwise
the legend will now take up a large portion of the plot area.

	`g has (`xs`ys;(600;500))   

The legend box can also be repositioned within the plot area.

	`g has (`legend;`br)          Bottom right	
	`g has (`legend;`tc)          top center
	`g has (`legend;`tl)          top left (where we started)

Other settings are `tr, `bl, and `bc. (Note that we just set the `legend
attribute for the graph g, while just above are settings of the `legend
attribute for trace sets.) In addition, you can specify the position of
the upper left corner of the legend box, as percentages of the
horizontal and vertical lengths of the graph window. They take effect
when `legend has the value `xy:
	`g has (`xlegend `ylegend;(25;75))   the (x,y) percentages
  	`g has (`legend;`xy)		    

Now that the `legend attribute has been set to `xy, settings of `xlegend
and `ylegend take effect immediately:

	`g has (`xlegend;50)

Note that the legend cannot be partially hidden by the choice of
`xlegend and `ylegend. For example, if these coordinates are set to
(95,95) one might expect that only the upper left corner of the legend
would be visible. However, this is not the case:

	`g has (`xlegend `ylegend;(95;95))   the (x,y) percentages

The specified position is respected as far as possible, consistent with
keeping the legend completely visible.

The values of `xlegend and `ylegend are integers between 0 and 100 or,
alternatively, fractions between 0 and 1.

The legend can also be strung out horizontally:

	`g has (`legend;`tl) 		 
	`g has (`legendstyle;`hor)

The original configuration is:

	`g has (`legendstyle;`ver)

Other attributes control the colors and font of the legend.
Specifically, the background color of the legend:

	`g has (`legendbg;`white)

the foreground color, or color of the text in the legend:

	`g has (`legendfg;`blue)

the font of the text in the legend:

	`g has (`legendfont;"Times-Roman-15")
and, finally, even the pixel width of the legend's highlight and shadow
thicknesses (the defaults are 1):

	`g has (`legendshadowthickness;3)
	`g has (`legendhlthickness;2)

The legend can be made to blend into the graph:

	`g has (`legendbg;0`bg of `g)
	`g has (`legendshadowthickness;0)
	`g has (`legendhlthickness;0)
The legend can be removed by setting the legend position to `none:

	`g has (`legend;`none)

2f. x-Axis and y-Axis Titles

Titles for axes are two other components that do not appear in the 
default form of a graph.     

	`g has (`xtitle;"0 to 9")      	    
	`g has (`ytitle;"0 to 81")	   

Let's make them big enough to be easily seen:

	`g has (`xtitlefont;"Times-Roman-25")    
	`g has (`ytitlefont;"Times-Roman-25")    

Note that the x-axis title is positioned below the x-axis and the y-axis
title is above the y-axis. The y-axis title can be repositioned
vertically along the y-axis as follows:

	`g has (`ytitlestyle;`ver)	    

The axis titles can be justified:

	`g has (`xtitlejustify;`left)
	`g has (`xtitlejustify;`right)
	`g has (`xtitlejustify;`center)
	`g has (`ytitlejustify;`top)
	`g has (`ytitlejustify;`bottom)
	`g has (`ytitlejustify;`center)

Return to the original position with:

	`g has (`ytitlestyle;`hor)	   

The y-axis title can now be justified right and left:

	`g has (`ytitlejustify;`left)
	`g has (`ytitlejustify;`right)
	`g has (`ytitlejustify;`center)

Notice that there seems to be no difference in right and center
justification of the y-axis title. We can set the left margin so you can
see the difference:

	`g has (`left;20)
	`g has (`ytitlejustify;`left)
	`g has (`ytitlejustify;`right)
	`g has (`ytitlejustify;`center)
	`g has (`left;0)

We'll have more to say about margins later. The colors of the axis
titles can be set separately:

	`g has (`xtitlefg;`red)
	`g has (`ytitlefg;`yellow)

2g. Axes

Most of the settable attributes in good graphics packages deal with
axes, and this one is no different. There are four parts to an axis: the
rule which extends the length of the axis; the tick marks; the labels on
the tick marks; and the grid lines of the graph associated with the tick
marks. Each of these parts can be controlled with the appropriate
attributes. In addition, there are a few attributes that affect the
overall appearance of the axes.

First of all, we can control the color of the axes:

	`g has (`xfg;`yellow)    		 
	`g has (`yfg;`red)    		 

We can also control the thickness of the axis rules:

	`g has (`rulewidth;2)  	

As you can see, the thickness of both axes rules and tick marks are affected.
The units of the axis thickness are pixels.

A rule width of 0 has special meaning. Although it looks no different
from 1 on the screen, it has the effect of drawing the rules more
efficiently, and more importantly, perhaps, there is a noticeable
difference when a graph is printed.

	`g has (`rulewidth;0)  	

More interesting, perhaps, is the control one has over the style of the
axes. We will go through all the possibilities. For example, we can have
an x-axis only or a y-axis only.
	`g has (`axis;`x)		
	`g has (`axis;`y)		
	`g has (`axis;`xy)		

Vertical grid lines can be placed at the major x-axis tick marks.

	`g has (`grid;`x)	
Likewise, horizontal grid lines can be placed at the major y-axis tick

	`g has (`grid;`y)

Both horizontal and vertical grid lines are also possible:
	`g has (`grid;`xy)     

Both the widths (in pixels) and colors of the gridlines can be set:

	`g has (`gridwidth;2)
	`g has (`gridfg;`green)

A grid width of 0 has the same effects as a rule width of 0:

	`g has (`gridwidth;0)

There is a `rule attribute whose default value is `axis, meaning that
any axes that appear have rules. This attribute can also be set to
values like those for `grid, indicating which axes have rules. For
example, we can have a graph with an ordinary y-axis and just the x-axis
	`g has (`axis;`y)
	`g has (`rule;`xy)

An interesting effect is obtained by removing the rule from the y-axis:

	`g has (`rule;`x)

The graph can have ascending values or descending values:

	`g has (`ymode;`descend)
	`g has (`ymode;`ascend)

2g1. Axis Tick Marks

We will use an uncluttered graph to illustrate the details of tick-mark
and label attributes.

	$off                  Exit from A+

Press F4 to start A+ again, then move the cursor back to the tutorial
buffer, on the next line.

	$load s

	v 53 14 27 2 31 85 30 11 67 50
	show `g is `graph
	`g has (`xs`ys;(300;200))      This may have no effect, i.e.,
				       this may be the default size.

The lengths of both the major and minor tick marks can be set. The unit
of length is pixels. Let's first look at the default values to get a
sense of their scale.

	`xmajorticksize of `g		
<  10					 A+ output
	`xminorticksize of `g		
<  6					 A+ output

The tick marks can be made smaller, leaving a larger plot area. For

	`g has (`xminorticksize;2)	
	`g has (`xmajorticksize;5)	

The number of minor tick marks that appear between major tick marks can
be specified, for the x-axis and y-axis separately. In the present
example, 4 minor tick marks between major tick marks on the y-axis would
put a mark at every increment of 5:
	`g has (`yminorticks;4)

It often improves the appearance of a graph to remove the minor tick
marks, which can be done by setting their number to 0. For example:

	`g has (`xminorticks;0)

The number of major tick marks can also be specified, if somewhat
indirectly, by specifying the increment between major tick marks. For

	`g has (`yinc;40)
	`g has (`xinc;2)

And, finally, we can control the style of the tick marks: pointing away
from the plot area, into the plot area, or straddling the axis:

	`g has (`ytickstyle;`in)      The tick marks point inwards
	`g has (`xtickstyle;`inout)   The tick marks straddle the axis
	`g has (`xtickstyle;`out)     The tick marks point outwards 
The latter is the default. Graphs with tick style `in are effective
because the plot area is larger, and the inward pointing ticks rarely
decrease the usable plot area.

2g2. Axis Labels

We have control over two aspects of the axis labels: the font in which
they are set and their format.

At this point it is useful to switch to an example with realistic data.

	$off                  Exit from A+

Press F4 to start A+ again, then move the cursor back to the tutorial
buffer, on the next line.

	$load s
	x0 "/usr/local/aplus-fsf-4.18/doc/tutorials/graphs/graph_data.m";

This data is high, low, open, close information taken at, roughly, 
5-minute intervals over a 5-day period in Tokyo. The market day is
partitioned into 5-minute increments and x contains one row for each
period. A timestamp, which is in column 0, is the time of the last
reading for the 5-minute period in which it falls. The timestamps are
Unix timestamps.

The data in columns 1 through 4 of a given row are associated with the 
5-minute time period in which the timestamp in column 0 lies. They
represent, starting with column 1, the high value of all readings taken
during the 5-minute period, the low value, the open, and the close.
At this point we need only one of the traces:

	yx[;0 1]
	show `g is `graph
	`g has (`xs`ys;(300;200))      This may have no effect, i.e.,
				       this may be the default size.

You will notice that the data on the graph appears clustered in several
areas, and these clusters are connected by relatively long line
segments.  The clusters represent periods of market activity, while the
long line segments represent periods during which the market is closed.
In applications, these long segments would be factored out to give the
graph a uniform appearance, but that is not a concern here.

Let's look at the timestamp format on the x-axis labels first. Since
this is daily data, we start with the seven-day format, which uses
abbreviated names for the days:

	`g has (`xlabelout;`day7_u)

Note that the major tick marks indicate the beginning of every other
day, and the minor tick marks therefore mark the remaining days.

Let's look at days of the month or days of the year, which are integers
indicating the number of days since the beginning of the month or year:
	`g has (`xlabelout;`day31_u)

The minor tick marks now represent half days.
	`g has (`xlabelout;`day365_u)

Once again, the minor tick marks represent days.

The time span between major tick marks, and therefore the meaning of the
minor tick marks, depends to a large extent on the sizes of the labels,
because these sizes determine the number of labels the graph can
accommodate.  We have some indirect control over the number of labels
that appear and their format, because we can specify the font for the
labels. (More direct control is described below in "2g3. Controlling Tick
Mark Location and Label Formatting".) For example:

	`g has (`xlabelout;`day7_u)

Check the default label font, and then set it to a smaller pixel size.

	`xlabelfont of `g			
	`g has (`xlabelfont;"Helvetica-Bold-7") 

You should now see a major tick for each weekday. Of course the labels
are very hard to read. Another possibility is to simply choose the size
of the graph appropriately. First reset the axis font:

	`g has (`xlabelfont;"Helvetica-Bold-12")

and then resize the graph:

	`g has (`xs`ys;(800;300))

There are two month-only formats, one that uses names and the other the
numbers 1 through 12, and there are two year-only formats using 2 digits
and 4 digits. These formats are not particularly interesting for data
which is all from the same month, but for completeness here they are:

	`g has (`xlabelout;`m_u)
	`g has (`xlabelout;`m12_u)
	`g has (`xlabelout;`y2_u)
	`g has (`xlabelout;`y4_u)

The next format gives a text form of day, month and year, while the four
that follow give various abbreviated forms:

	`g has (`xlabelout;`mdy_u)
	`g has (`xlabelout;`mdy2_u)
	`g has (`xlabelout;`mdy4_u)
	`g has (`xlabelout;`dmy2_u)
	`g has (`xlabelout;`dmy4_u)

The remaining time formats are hours, minutes, and seconds, so to get
major tick marks with these units, restrict the data to a single day, as


The market hours are 9:30 to 11:00 and 1:30 to 3:30. Test the following 

	`g has (`xlabelout;`hrmin)
	`g has (`xlabelout;`hrmin24)
	`g has (`xlabelout;`hr)
	`g has (`xlabelout;`hr24)

To get major tick mark labels in minutes, further restrict the data as


This data is not fine enough to exhibit variations in seconds, but here are
the remaining time formats:

	`g has (`xlabelout;`min)
	`g has (`xlabelout;`sec)
	`g has (`xlabelout;`minsec)
	`g has (`xlabelout;`hrminsec)
	`g has (`xlabelout;`hrminsec24)

Finally, you can remove the labels altogether:

	`g has (`xlabelout;`)

In addition to the primary x-axis labels, there are sublabels that
provide a second level of text. Sublabels are useful when all the label
text does not fit conveniently on one line, and we will see examples of
this in the next section. For now, go back to the original graph of this

	yx[;0 1]
	`g has (`xs`ys;(300;200))  
	`g has (`xlabelout;`day31_u)
	`g has (`xsublabelout;`m_u)       The sublabels automatically appear. 

One last point on x-axis formatting. The labels and sublabels can be
justified relative to the tick marks:

	`g has (`xlabeljustify;`right)
	`g has (`xlabeljustify;`left)
	`g has (`xlabeljustify;`center)

	`g has (`xsublabeljustify;`right)
	`g has (`xsublabeljustify;`left)
	`g has (`xsublabeljustify;`center)

The sublabels are removed in the same way as labels:

	`g has (`xsublabelout;`)

Turning now to the y-axis, which in this example represents bond prices,
there are the following formats:

	`g has (`ylabelout;`32nd)
	`g has (`ylabelout;`64th)
	`g has (`ylabelout;`128th)
	`g has (`ylabelout;`320th)
	`g has (`ylabelout;`328th)

y-axis labels can also be justified:

	`g has (`ylabeljustify;`top)
	`g has (`ylabeljustify;`bottom)
	`g has (`ylabeljustify;`center)

Finally, we have three generally applicable label formats. For
convenience we will use the present example for illustration, even
though these formats are not appropriate for the data. The first of the
three displays the decimal part of the number as a fraction:

	`g has (`ylabelout;`frac)

The last two provide conventional floating point and fixed point
	`g has (`ylabelout;`float)
	`g has (`ylabelout;`fixed)

The number of decimal digits that appear can be specified for the fixed

	`g has (`ylabelout;(`fixed;2))

The default label format is `float.

2g3. Controlling Tick Mark Location and Label Formatting

In addition to the variety of label formats illustrated above, you can
also specify your own format, much as you specify the format of any data
that appears on the screen. Furthermore, you have complete control over
the tick mark locations and the text of the labels for those tick marks.
Let's start with a clean slate.

	$off                  Exit from A+

Press F4 to start A+ again, then move the cursor back to the tutorial
buffer, on the next line.

	$load s

The screen management system provides ways for programmers to control
the formatting of tabular data on the screen. Each array on the screen
can be controlled separately. The control mechanisms for data on the
screen are:

	 a formatting parameter for the dyadic primitive format 
	  function  can be specified for an array, and will be applied
	  to every displayed element;
	 a formatting parameter for the system function _fmt can be 
	  specified, and will be applied to every displayed element;
	 a function can be specified that will be called for every
	  displayed element.

The same rules apply to labels on tick marks, only now the data elements
being formatted are tick values. For example:

	show `g is `graph
	`g has (`ylabelout;6.3)    	 A valid format parameter of 

A second example:

	`g has (`ylabelout;"f10.4")	 A valid format parameter of _fmt

`ylabelout can also be specified as a function. See the discussion of
the of the `out attribute in the A+ Reference Manual.

Complete control over ticks and tick labels is provided by the `ylabel
attribute. We'll begin by adjusting the window of the current graph
slightly, just to make sure the bottom and top ticks that are created
below will appear.

	`g has (`ymin `ymax;(97.9;99.1))

The value of the `ylabel attribute is a four-element nested vector of
the form


- ticks is a numeric vector representing the tick values, or locations
on the axis where the tick marks occur;
- labels is either a nested vector of character vectors, where ilabels
is the label for the tick value i#ticks, or a character matrix, where
i#labels is the label for the tick value i#ticks;
- sizes is a vector of numbers between 0 and 1, where the length of the
i-th tick mark is i#ticks times the current size of the major ticks
(that size is controlled by the `majorticksize attribute);
- widths is a vector of integers, where i#widths is the width, in
pixels, of the grid line at the ith tick mark.
Continuing the previous example:

     	size0 .2 .4 .6 .8 1
     	width0 1 2 3 4 5
     	`g has (`ylabel;(ticks;labels;size;width))

You should see tick marks at locations 98, 98.2,...,99 with labels "one"
through "six". The tick marks lengths are 0, 2,...,10 pixels (10 is the
value of the `majorticksize attribute). And, finally, there are grid
lines of width 0, 1,...,5 pixels. As you can see, the possibilities are
boundless for creating major and minor tick marks with various label and
grid line strategies.

In this example all four quantities have the same length, but that is
not required. If more labels are given than there are tick marks, the
extras are ignored. If fewer are given, the missing ones are considered
to be blank.  In particular, tick marks without labels are obtained by
specifying one label, and making that one all blank.

     	`g has (`ylabel;(ticks;" ";size;width))

If either size or width has fewer elements than ticks, those elements
are used cyclically, in the manner of the A+ Reshape primitive.

     	`g has (`ylabel;(ticks;labels;size[1 3 5];width[2 4]))

It is not necessary to specify all four components; only ticks must be
present. If labels is missing, the default format is used, or the
setting of the labelout attribute if there is one.

     	`g has (`ylabel;(ticks;size[1 3 5];width[2 4]))

If only one of size and width is present, which it is can (almost)
always be determined by the values: widths must be whole numbers, while
sizes are 0, 1, or fractions in between. The one ambiguous case is a
vector of 0's and 1's, and that is taken to be a width specification.

     	`g has (`ylabel;(ticks;0 1))
Like `ylabelout, `ylabel can be assigned a function that will be called
whenever tick marks and labels are needed for a graph, e.g., each time a
graph is zoomed (see "5a. Zooming"). When called, the function must
produce a four-element vector like the one described above.

There are interesting interactions between xlabel settings and
sublabels.  Suppose the x-axis in the present example represents dates
and define:

     `g has (`xlabel;(210;10 3"JanAprJulOct"))

Each group of labels "Jan through "Oct" represents a year, and we can
use the sublabel attribute to put year designations under the groups:

     `g has (`xsublabel;(3 11 19;3 4"199219931994"))

When a graph is zoomed, a section of the view is blown up to fill the
entire plot area. If `ylabel is assigned a fixed value, as in the above
example, then these are the only tick marks that can be used for the
zoomed view. Some of them may fall in the range of the zoomed view, but
some may not. If the area of the original graph chosen for zooming
contained none of these tick values, no tick marks would appear. But if
`ylabel is assigned a function, that function will be called to
determine new tick locations and labels for the zoomed view.
There are several graph attributes that can be referenced in the `ylabel
function that produce information helpful in determining tick values and

	`yextent of `g

is a three-element vector containing the minimum value along the y-axis,
the maximum value, and a scale factor. As a result of the last
expression you should see:

<  97.9 99.1 107.5

although the third element might be different. 97.9 is the minimum value
and 99.1 the maximum value along the y axis, which we set above. The
scale factor is such that


is the length of the y-axis in pixels. Resize the graph, evaluate

	`yextent of `g

again, and you should see a new scale factor.

It should be easy to understand that the minimum and maximum values are
necessary for determining tick values. But what is the point of the
scale?  Well, you don't want so many tick values that the labels overrun
each other.  Since you know the length of the y-axis in pixels, once you
determine the number of tick marks, you know the distance between tick
marks in pixels.  The labelheight attributes tell you the height in
pixels of all labels, and therefore you can determine whether or not
they overlap. For example:

	`xlabelheight of `g

Analogously, xlabelwidth attributes tell you the width of labels in
pixels, which can be used, for example, to see that x-axis labels don't
overrun one another. However, the situation is more complicated for
x-axis labels, since both the label texts and font characters can have
different widths.  Therefore, to determine the width of a proposed
label, the text of the label is part of the query:

	(`xlabelwidth;"testlabel") of `g

It is also possible to determine the widths of several labels at once,
either as the rows of a character matrix or as the elements of a nested
vector of character vectors:

	(`xlabelwidth;3 5"one  two  three") of `g
	(`xlabelwidth;("one";"two";"three")) of `g

Now that we have specified the y-axis labels and can determine their
widths, we can easily create a nice effect for these labels:

	`g has (`ylabeljustify;`top)
	`g has (`ymajorticksize;/0(`ylabelwidth;labels) of `g)
	`g has (`ylabeljustify;`bottom)

2h. Alternate Axes

The last two graph components have to do with arranging traces with
different scales on the same graph. Neither of these components appear
in the default form of a graph. The components are the alternate x-axis
and the alternate y-axis. We begin by demonstrating how these components
can be made to appear and disappear.

The default axis configuration consisting of an x-axis on the bottom and
a y-axis on the left can be specified as follows:

	`g has (`axis;`std)

It is also possible to have a alternate x-axis at the top of the graph
and an alternate y-axis to the right. In fact, any or all of these four
can be used, or none. For example:
	`g has (`axis;`box)           All four axes
	`g has (`axis;`xYy)           Three axes; the alternate x-axis is

Instead of `xYy, as in the last example, any of `xyY, `Yxy, `xy, `YX,
etc. can be used, and the axis designators (x, y, X, Y) can appear
in any order.
	`g has (`axis;`)              No axes.

There are also interesting effects when just the rules for certain axes
are used. For example:

	`g has (`axis;`std)           Standard x-axis and y-axis.
	`g has (`rule;`XY)	      Include rules on the top and right.
	`g has (`axis;`)              No axes.
	`g has (`rule;`box)	      Enclosing box made up of axis rules.

In these examples the alternate axes have the same scales as the
corresponding default axes, but in practice they are most useful when
they have different scales. This is because it is often useful for
traces with values in different scales to appear on the same graph: for
example, two traces of bond prices and another of their spreads, where
the prices are plotted on the y-axis and the spreads on the alternate

	$off                  Exit from A+

Press F4 to start A+ again, then move the cursor back to the tutorial
buffer, on the next line.

	$load s

	p198.8 99.6 101.3 99.1 100.7   
	p2101.8 101.2 99.9 100.5 99.6
	g`p1 `p2 `s
	show `g is `graph
	`p2 has (`linecolor;`yellow)
	`g has (`xs`ys;(300;200))      This may have no effect, i.e.,
				       this may be the default size.

You can see that the two price traces are clustered around 100 and the
spread is clustered around 0, which is to be expected. When they are all
plotted on the same scale, the graph has very poor resolution. Even
worse, it does not make sense to plot them on the same scale.

The spread should be plotted on a separate graph, or on a separate scale
on the same graph.  The alternate y-axis can be used for this purpose,
as follows:

	`s has (`yaxis;`Y)   

Setting the `yaxis attribute for a trace set to be the alternate y-axis
modifies the graph so that the trace set is plotted on a second,
independent y-axis appearing on the right of the plot area. Note that
removing the spread trace set from those to be plotted on the left
y-axis enabled that axis to be rescaled.
The default value for the `yaxis attribute is `y, which causes the trace
set to be plotted on the original left y-axis.

	`s has (`yaxis;`y)
	`s has (`yaxis;`Y)

Note that specifying `yaxis to be the alternate y-axis caused that axis
to appear. The automatic appearance of the alternate y-axis is due to
the setting of the `axis attribute for g, which is `std, the default.
For any other setting, the traces will be rescaled but alternate axes
will not appear automatically.

	`s has (`yaxis;`y)   
	`g has (`axis;`xy)     The graph looks the same as the `std setting.
	`s has (`yaxis;`Y)     Rescale the traces, but no alternate y-axis.

	`s has (`yaxis;`y)   
	`g has (`axis;`std)
	`s has (`yaxis;`Y)     Rescale the traces,and get alternate y-axis.

The `std value for the axis attribute can be said to be passive,
however. Setting axis to `std does not cause the graph to be redrawn:

	`g has (`axis;`xy)     Active: removes the alternate y-axis.
        `s has (`yaxis;`y) 
	`s has (`yaxis;`Y)     Rescale the traces, but no alternate y-axis. 
	`g has (`axis;`std)    Passive: still no alternate y-axis.
	`p2 has (`linecolor;`yellow)   Forced redrawing shows the axis.

Grid lines can drawn for either the y-axis or the alternate y-axis, but
not both:

	`g has (`grid;`y)
	`g has (`grid;`Y)
	`g has (`grid;`Yy)
	`g has (`grid;`yY)
All attributes for the alternate y-axis are the counterparts of y-axis
attributes, and therefore are not illustrated here. They are all listed
at the beginning of the tutorial.

The x-axis can be controlled in the same was as the y-axis. Again, we
content ourselves with the listing of the attributes at the beginning of
the tutorial, except to note these combined forms:

	`g has (`grid;`xy)
	`g has (`grid;`xY)
	`g has (`grid;`Xy)     Accepted, but no vertical grid lines at
	`g has (`grid;`XY)       this time, because no alternate x-axis.
	`g has (`grid;`none)

2h. Zero Axes

An additional one or two axes can be included on a graph, each passing
through 0 on the appropriate axis. The values of the zero attribute are
`none, `x, `X, `y, `Y, `xy, `xY, `Xy, and `XY:

	`g has (`zero;`xY)

The width, color, and style of these axes can be controlled:

	`g has (`zerowidth;5)
	`g has (`zerofg;`seagreen)
	`g has (`zerostyle;`dash3)

The values for width are 0 through 10. Those for style are `dot1 through
`dot5, `dotdash1 through `dotdash5, `dash1 through `dash5, and `solid.

	`g has (`zero;`none)

3. Trace Styles

So far we have dealt only with graphs composed of line segments. In this
section the other graph styles available will be illustrated. We will
use the same data as earlier on.

	$off                  Exit from A+

Press F4 to start A+ again, then move the cursor back to the tutorial
buffer, on the next line.

	$load s

	x0 "/usr/local/aplus-fsf-4.18/doc/tutorials/graphs/graph_data.m";

We can restrict our attention to a single day.

	yx[;0 1]
	show `g is `graph
	`g has (`xs`ys;(800;300))
     	`g has (`xlabelout;`hrmin24)
	`g has (`ylabelout;`32nd)

The default graph style is `line. The first set of variations in style
are scatter, line-scatter, and bar chart:
	`y has (`style;`scatter)       
	`y has (`style;`linescatter)     `ls for short is accepted
	`y has (`style;`step)
	`y has (`style;`stepscatter)     `ss for short is accepted
	`y has (`style;`bar)

Just as you saw for `line, if the trace set has more than two columns
then more than one trace is drawn. For example:

	yx[;0 1 2]

There are now two visible bar graphs, colored the same as if they were
line or scatter plots.

	`y has (`style;`line)
	`y has (`style;`bar)

However, in the case of bar graphs, these colors are default fill
colors, not default line colors. We can set the fill colors:
	`y has (`fillcolor;`yellow `pink)

Note that the legend samples for the two traces appear to be quite
different from the traces themselves, in that fairly prominent red and
green borders appear in the legend, whereas the borders in the traces,
if they appear at all, may be narrow and faint. We can bring out the
borders in the traces by limiting the graph to fewer points.


The borders should be visible now. They have the same line color
characteristic that line graphs have:

	`y has (`fillcolor;`red `green)
	`y has (`linecolor;`yellow `pink)

Neither of these settings may be easy to see except in the legend, but
they still hold if we change the style of the graph:
	`y has (`style;`scatter)

Note that the fillcolor setting is used for the symbols in a scatter
plot; in a linescatter plot, the linecolor settings apply to the line
segments and the fillcolor settings apply to the symbols.

	`y has (`style;`linescatter)

The symbols that appear in scatter and linescatter traces can be any of
the values shown in the following statements:

	`y has (`symbol;`square `squarefilled)
	`y has (`symbol;`circle `circlefilled)
	`y has (`symbol;`diamond `diamondfilled)
	`y has (`symbol;`cross `xsym)
	`y has (`symbol;`triangle `trianglefilled)
	`y has (`symbol;`star)           If too few, used cyclically.

The size of the symbols (in pixels) can be specified:

	`y has (`symbolsize;50)
	`y has (`symbolsize;10)

The symbol can also be set to any character vector or symbol:

	`y has (`symbol;"Vertex")
        `y has (`symbol;`Open`High)

This is where the font attribute of the trace set comes into play.

	`y has (`font;"Courier50")        This may take a moment to do.
	`y has (`symbol;`cross`circle)
Let's return to the bar graphs:

	`y has (`style;`bar)

The border in a bar graph is only 1 pixel thick, and the thickness
cannot be changed. In a graph with many bars, the border may even be

	yx[;0 1]     No borders
	y5y         Borders present

One last point about these trace styles. The bars and their borders in a
bar chart can be individually colored using the `gradient attribute,
which cycles through the specified colors, and if none were specified
(i.e., a null specification) then through the colors in s.FILLCOLORS and

	`y has (`gradient;1)
	`y has (`fillcolor;)
	`y has (`linecolor;)

(The borders do not show now because the default values of s.FILLCOLORS
and s.LINECOLORS are the same.)

The gradient attribute applies to scatter plots as well:

	`y has (`style;`scatter)

(Of course, bars and symbols can be colored individually by making the
fillcolor and linecolor attributes of the trace set functional; then the
colors can be related to the data values. See "Functional Attributes" in
the A+ Reference Manual).
The remaining graph styles to be illustrated with this data take
advantage of the full range of high, low, open, and close information in
the data.  We will stay with the bar chart for the moment:
	`y has (`style;`bar)
	`y has (`gradient;0)
	`y has (`fillcolor;`red `blue `white `green)

You should see four bar chart traces. The first, in red and appearing on
the left in each group, is the open for time period. The second is the
high and is in blue, the third is the low and is in white, and the
fourth is the close and is in green. These four traces can be combined
in one high-low-open-close chart:

	`y has (`linestyle;`solid)	
	`y has (`linecolor;`red)
	`y has (`style;`ohlc) 
Each line extends from the low to the high and has ticks pointing left
at the opening and right at the close. This style often looks better
with wider lines:

	`y has (`linewidth;3)

Note that the line width also applies to the length of the open and
close tick marks on the vertical line segments.

The other style that uses the complete high, low, open, and close data
is candlestick.

	`y has (`style;`candle)

Again, each one extends from low to high, but the range between open and
close is indicated by a box, the candle (the rest being the wick). Since
there is only one line color, if the close exceeds the open, the candle
is hollow; otherwise it is filled.  The fill color can be specified, but
using the `linecolor attribute instead of `fillcolor:

	`y has (`linecolor;`red `pink `white `green)

As you can see, the first color, red, is the color of the fill when the
open exceeds the close, the second is the color of the vertical line
segments (the wicks), the third is the border color of the filled areas,
and the fourth is the color of the fill when the open is less than the
close. Because the line color attribute is responsible for all color
variations, it is easy to switch meaningfully among graph types.

	`y has (`style;`ohlc)    
	`y has (`style;`scatter `line `linescatter `bar)

When the value of `style has more than one element, it must be
restricted to styles that require only one y-coordinate, i.e., one
column of the trace-set matrix.

If fewer than four values are supplied for these attributes, they are
used cyclically. If we then set two styles on the current graph:

	`y has (`style;`line `bar)

we see that the first and third traces are line graphs, while the second
and fourth are bar graphs.

Finally, we have high-low, high-low-close, and close graphs. High-low
graphs naturally use three-column matrices, high-low-close four-column,
and close graphs two-column. These styles can be applied to the current
five-column y, however:  the high-low graph will use columns 0, 2, and
3; the high-low-close graph will use columns 0, 2, 3, and 4; and the
close graph will use columns 0 and 4.

	`y has (`style;`highlow)        `hl is accepted for short
	`y has (`style;`highlowc)       `hlc is accepted for short
	`y has (`style;`close)          `c is accepted for short

In the case of a high-low graph, the data y can also have four columns,
in which case the first three are used as the x-coordinates, highs, and
lows.  For close graphs the data can also have three or four columns,
and the first and last column are used in each case.

It is often useful in complicated graphs to be able to remove some
traces at certain points in an application, and then later put them
back.  This can accomplished by setting their style to `none, or simply
` for short.
	`y has (`style;`scatter `line `linescatter `bar)
	`y has (`style;`scatter `line `none `bar)
	`y has (`style;`scatter `line `linescatter `)

Finally, there is a style for drawing arbitrary line segments, and two
other styles related to filling in areas, and for those we will use
different traces.

	$off                  Exit from A+

Press F4 to start A+ again, then move the cursor back to the tutorial
buffer, on the next line.

	$load s

There are times when you want a trace made of disconnected line
segments.  This can be done when the number of line segments is small by
using separate traces, but even then the set of lines cannot be moved or
copied as a group. The segment style solves this problem. The argument
must be a two-column matrix of coordinate points. The points are grouped
in pairs to form line segments: the first two rows form the first
segment, the second two rows the next segment, and so on. For example:

	x10 20 0 1 1 0 1 1 2 0 2 1 3 0 3 1 4 0 4 1 5
        5 2 2x               Show the segments even better.
	show `g is `graph

In this view `x is an ordinary line trace. But:
	`x has (`style;`segment)

Moving on to the styles that fill in areas:

	`x has (`style;`fill)

The fill style connects the first and last points of a trace and then
fills in the resulting closed polygon with the fillcolor.

	`x has (`fillcolor;`blue)

You should now be able to distinguish the fillcolor from the linecolor
border, but even so, for this example we will set:

	`x has (`linecolor;`white)

There is a complement to this graph, obtained by filling in underneath
the curve:

	`x has (`style;`area)

Both areas can be put on one graph.

	`x has (`style;`line)
	`x has (`style;`fill `area)
	`x has (`fillcolor;`red `blue)

Now give both traces the `fill style:

	`x has (`style;`fill)

Since both traces have the same values, only one shows in the graph.
This is not true, however, if they are both `area graphs:

	`x has (`style;`area)

Area graphs are cumulative; the top of the red graph actually represents
the trace x[;1] plus the trace x[;2]. We can see this by making a third
trace which is this sum, and displaying it as a `line graph by default.
It will lie along the top of the red area:

	yx[;0],@0 x[;1]+x[;2]

If we made this separate trace set an area graph, it would be cumulative

     	`y has (`style;`area)
     	`y has (`style;`line)

A variation of the area graph is the stack graph, which is a stacked bar

	`x has (`style;`stack)

3a. Text Traces

Some of the traces on a graph can be textual, and thereby used to
annotate various aspects of a graph.

	$off                  Exit from A+

Press F4 to start A+ again, then move the cursor back to the tutorial
buffer, on the next line.

	$load s

	x0 "/usr/local/aplus-fsf-4.18/doc/tutorials/graphs/graph_data.m";

	yx[;0 1]
	show `g is `graph
	`g has (`xs`ys;(800;300))
     	`g has (`xlabelout;`day7) 
	`g has (`ylabelout;`32nd)

All trace sets have titles, but only those titles associated with
certain trace sets are visible: namely, trace sets whose style is `text
and which have only one coordinate point. (Actually, although it would
normally be pointless, the trace set can contain more than one trace and
points can be added -- and ignored by A+ -- after the title is
displayed.) For example:

	z1 2719900000 107.3
	`z has (`style;`text)

Note that a text trace does not appear in the legend. The default title
of a trace set is its name, and you should now see "z" on the graph. We
can set the title to the name of the contract with the data y:

	`z has (`title;`Contract_JYU2)
	`z has (`title;"Contract: JYU2")

The appearance of titles can be modified by specifying their font and

	`z has (`titlefont;"Helvetica-Bold-20")
	`z has (`titlefg;`yellow)

The value of z, which is the coordinate of the title, marks the lower
left corner of the text.

4. Graph Attributes

The attributes illustrated here are the background color of a graph, the
coordinate window, and margins. We continue with the current example.

The color midnight blue is commonly used for the background color in
graphics packages:

	`g has (`bg;`midnightblue)

Now, however, the axes and legend must be recolored in order to be
visible. The foreground color fg applies to all axes, axis labels,
legend titles, and legend border whose colors have not been explicitly

	`g has (`fg;`white)

Another interesting background color is:

	`g has (`bg;`green4)
	`g has (`fg;`black)

The color name green, and many others (see the A+ Reference Manual) can
be modified with the digits 1 through 4, indicating the degree of
grayness in the color. green4 is the most gray of the four, and muted
colors are best for graph backgrounds.

	`g has (`bg;`green3)
	`g has (`bg;`green2)
	`g has (`bg;`green1)
	`g has (`bg;`green4)
	`g has (`fg;`white)

The margins of the area consisting of the plot area, axes and labels,
and axis titles can be controlled; their values are in percentages,
i.e., integers between 0 and 100, or nonnegative fractions less than 1.
First put axis titles on the graph:
	`g has (`xtitle;"x-axis title")
	`g has (`ytitle;"y-axis title")
	`g has (`ytitlestyle;`ver)

	`g has (`left;20)
	`g has (`left;0)
	`g has (`right;0.2)
	`g has (`right;0)
	`g has (`bottom;20)
	`g has (`bottom;0)
	`g has (`top;0.2)
	`g has (`top;0)

By default, the extreme values of traces touch the boundaries of plot
areas; however, there is a margin around the plot area that can be
specified, in percentages or fractions. For example:

	`g has (`xleft;5)
	`g has (`xright;0.05)
	`g has (`ybottom;5)
	`g has (`ytop;0.05)

Note that the plot area for traces whose scales are the alternate axes
can be specified separately using `Xleft, `Xright, `Ybottom, and `Ytop.

The coordinate window can also be specified. This is particularly useful

    lining up traces on the alternate y-axis with those on the y-axis;

    having more direct control, in terms of data, over the margins to 
     accommodate new data.

The lower left corner has coordinates (`xmin,`ymin) and the upper right 
corner has coordinates (`xmax,`ymax).

	(/y),/y                     xmin, ymin, xmax, ymax.
 719746439 106.59 720372715 107.54    The output is reproduced here 
                                        for convenience.

These values define the default coordinate window. If we set the window
to these values, the trace will once again fit tightly in the window.

	`g has (`rule;`box)
	`g has (`xmin `ymin `xmax `ymax;(719746439;106.59;720372715;107.54))

Now, move the mouse pointer to the graph and press any one of the arrow
keys.  As you see, the graph window moves over the graph. (If you click
the key too quickly and the window keeps moving, just press any key to
stop it.) This is particularly useful for time-series data. The window
can be set to show only the most important part of the series, while the
user can still see the rest by using the arrow keys.

If only `xmin and `xmax have been set, then only horizontal motion is
possible, and if only `ymin and `ymax have been set, then only vertical
motion is possible.

5. User Interactions

A+ graphics provides a rich set of user interactions for customizing the
display, editing the traces (and thereby the data), and examining the
details of the traces.

	$off                  Exit from A+

Press F4 to start A+ again, then move the cursor back to the tutorial
buffer, on the next line.

	$load s

	x0 "/usr/local/aplus-fsf-4.18/doc/tutorials/graphs/graph_data.m";

	`g is `graph
	`g has (`xs`ys;(800;300))
     	`g has (`xlabelout;`hrminsec)
        `g has (`xsublabelout;`mdy_u)
	`g has (`ylabelout;`32nd)
	z1 2719900000 107.3
	`z has (`title;"Contract: JYU2")
	`z has (`style;`text)
	show `g

5a. Zooming

In the current example, the useful data is in clusters which take up a
very small total area. We can use zooming to look at the details of one
of these clusters. Pick one and imagine a box around it. Move the
pointer to a corner of that imaginary box and press and hold the left
button. As you move the pointer a zoom box will appear, anchored to the
spot where the pointer was when the button was pressed, and attached to
the moving pointer. Move the pointer to a spot where the zoom box
encloses a cluster of data (or almost does) and release the mouse
button. The graph will be redrawn for the data within the zoom box only.
In this example there is no need to zoom further because the detail of
the cluster you enlarged should be apparent. When there are many points,
however, you may have to zoom several times to see all the details. Or
you may simply zoom again to neaten up the view, perhaps for printing.

While in the zoomed state you may want to look at the details of another
data cluster. One way to do this is to "unzoom" and then zoom again on
the new cluster. Another way is provided, however. While zoomed, the
graph window acts like a view window that can be moved over the original
graph using the arrow keys. Try it.
To "unzoom," i.e., to get back to the original graph, put the pointer on
the graph and double-click the left button.

If you start the zooming process and change your mind while manipulating
the zoom box, simply move the pointer near the anchor point or outside
the graph object entirely and release the button.

5b. Vertical Cursor and Cross Hairs

Zooming is only one way to examine the finer structure in a graph. There
are also vertical line and cross hair scans. Put the pointer on the
graph, and then press and hold the middle button. You will see three new
things: a vertical line running through the pointer; a modified legend
box that now displays y-coordinate values, in addition to trace
identifiers and trace segments; and a new box (next to the pointer) that
displays the x-coordinate.

As the pointer moves and the vertical line sweeps across the graph, the
line passes over x-coordinates for which there are data values.  As this
happens the values in the boxes change to the corresponding x-coordinate
and y-coordinate values. When the pointer is in an area outside the
range of the x-values, the displayed x-values vary continuously and
y-values are not shown.

You can display this variant of the legend even when you are not in the
vertical cursor mode. The displayed values in the legend will be those
in the last elements or rows of all the trace sets.

	`g has (`legendstyle;`lastvalue)

If you press the Control key and then press and hold the middle button,
you will see a somewhat different display: there are cross hairs instead
of a vertical line cursor; the legend is unmodified; both the x- and
y-coordinates are displayed in a new box, near the intersection of the
cross hairs. As the pointer moves, the intersection point of the
cross-hairs cursor moves with it and the changing coordinates are
displayed in the box. Both coordinates vary continuously in the
appropriate scale units as the cursor moves.

You can release the Control key once the cross hairs appear.

If there are alternate axes in use, then at any time that the vertical
or cross-hairs cursor is active, press the right button (in addition to
the middle) to see the alternate coordinates displayed in the moving box
as the cursor moves.

5c. Referencing a Graph, Line Trace, or Trace Point

Both a graph and its traces have refer events that can have active
callback functions. For example, define the following generic callback
function, which simply prints out the value of its static data argument,
the trace set (if any) associated with the event, and the (x-axis,
y-axis) coordinates of the pointer when certain events happen:

	gcbf{s;c;v}:(s;`selected of c,v;`coordinate of `g)	

(Use "`Coordinate of `g" when it is appropriate to query the coordinate
values of the alternate axes.) Set the refer attribute on the graph as

	`g has (`refer;(gcbf;`refer))

Now put the mouse pointer anywhere within the window border of the graph
and press the left mouse button. You will see `refer displayed in your
A+ session, showing that the refer event callback function was called,
together with the coordinates of the pointer position when the refer
attribute happened. In practice, the callback function would be defined
to do something meaningful.

A refer event can occur on a trace if
  its style is line,
  the trace is the only one in its trace set,
  the trace set has two columns, meaning that the x-coordinates are
    explicitly specified, and
  when the mouse pointer is on a line segment connecting two data 
   points, you double-click the left mouse button.
But first the trace must be selectable:

	yx[;0 1]
	`y has (`selectable;1)  
	`y has (`refer;(gcbf;`refertrace))

Now put the mouse pointer anywhere on a line segment and double-click
the left mouse button. You will see `refertrace displayed in your A+
session when you have successfully selected the trace; you will also see
that the pointer is now a red arrow when it is near the selected trace
and cross hairs away from it. Note that a new `refer appears just above
the `refertrace in your A+ session, because a refer event was caused by
the first click of the double click.

To revert to the unselected state, move the pointer onto the graph but
outside that object, and double-click the left button.

Finally, a referpoint event occurs when the mouse pointer is on a trace
point and the left mouse button is pressed:

	`y has (`referpoint;(gcbf;`referpoint))

The selected attribute of the trace will hold the (row index, column
index) of the referenced point.

Put the mouse pointer on a trace point and press the left mouse button.

Unlike refer events on traces, referpoint events occur no matter how
many traces there are in a trace set, and no matter what the trace
style. For example, set:

	`y has (`style;`ohlc)

and zoom the graph until you see distinct vertical segments. Put the
mouse pointer on one of the segments and press the left mouse button
to get a referpoint event.

To get back to where we were, move the mouse pointer off the traces and
double-click the left mouse button to undo the zooming. Then

	yx[;0 1]
	`y has (`style;`line)

5d. Selecting the Legend or a Text Trace.

Before a text trace can be selected, it must be made selectable:

	`z has (`selectable;1)

To select either the legend or a text trace, move the pointer onto it
and double-click the left button. The legend or text trace will then be
displayed with its background and foreground (i.e., text) colors

To revert to the unselected state, move the pointer onto the graph but
outside that object, and double-click the left button.

A refer event does not occur when the legend is selected.

Try selecting the legend and text trace and reverting to the unselected

5e. Repositioning the Legend and Traces

It is often useful to be able to reposition a legend or text annotation
that is covering an important part of a graph. There are also important
instances of repositioning numeric traces, such as trendlines.

To reposition an object, first select it and, with the pointer on the
object, press the left button and hold it. As you move the pointer,
either the object or an outline of it moves with the pointer. When you
release the left button, the object will stay in its last position.

Note that for any trace to be moved, it must be selectable; that is, its
selectable attribute must have the value 1. For numeric traces, only a
line trace that is the only trace in its trace set can be selected, and
therefore only such a numeric trace can be moved.

	yx[;0 1]

Try repositioning the legend and the traces. Note that when a trace is
moved, the value of the corresponding variable changes accordingly.

5f. Copying and Deleting Trace Sets

To copy a trace set, first select it, then put the pointer on it, and
press and hold the Shift key and then the left mouse button. Move the
pointer in order to position the copy; either the trace or an outline of
it will move with the pointer. When the left button is released, a copy
of the trace will appear at the last position of the pointer. (You can
then release the Shift key.) If you look at the graph variable g, you
will see that it now has a new element, in addition to `y and `z and
any elements from previous trace copies.  Execute the following to see
the new element:


A+ has created a new trace set variable to accommodate the copied text
trace, and chosen its name to be the first one available from a list
that begins `a, `b, `c, ... .  The new element of g is the symbol form
of that name.

To delete a trace, first activate the default delete behavior as

	`g has (`delete;1)

Now select a trace and press the Meta-Delete key (on an IBM keyboard,
Alt-Delete). The trace will disappear.  It has been deleted and its
variable removed from g.

As with repositioning, a trace must be selectable to copy or delete it.

5g. Editing and Creating Text Traces

Before we begin this section, restore the graph as follows:

	yx[;0 1]

You can edit a text trace on the screen. Simply move the pointer onto
the text, hold down the Meta (diamond) key (Alt on IBM keyboards), and
press the middle mouse button. An edit window will appear around the
text and you can now delete and insert characters. Press the Return key
when editing is complete. If you then examine the title of the text
trace you will see the modified text.

Try editing the text trace in the current example and then check:

	`title of `z

We can monitor the editing of text traces:

	`z has (`textactivate;(gcbf;`text_activate))

Edit the text again; when you press Return at the end of the editing
process the callback function is executed.

If the pointer is on the graph but not on the text of a text trace when
the Meta key and middle button are pressed, an empty edit box will
appear.  The text entered in this box will be the title of a new text
trace; the data of the new trace will be a matrix with shape 1 2 holding
the user coordinates of the pointer location when the edit box was

If you change your mind at any time while editing or creating a text
trace, simply press the Esc key to abort the editing and restore the
previous status.

Try bringing up the edit box for a new text trace and entering some
text. Press the Return key when entry is done. Then enter


Just as when copying text traces, you will find a new name (symbol) appended
to g.  Examine the title and data of the new text trace.

Text traces created in this way are automatically selectable, and therefore
can be moved, copied, and deleted.

You can use the mode attribute to initiate the creation of a text trace
at the point indicated by the coordinate attribute:

        `g has (`coordinate;719974911 107.45)
        `g has (`mode;`addtexttrace)

Now enter some text in the new trace, but don't press Return.

        `g has (`mode;`normal)

This setting of mode terminates interactive entry. The third setting is
`addtrace, which begins interactive entry of a line trace. A user can
terminate an interaction begun by a setting of mode, and an entry
initiated by the user can be terminated by a setting of mode.

You also have control over the behavior when users add, copy, and delete
text traces. For example, using the generic callback function defined
above we can monitor the adding and copying of text traces:

	`g has (`addtexttrace;(gcbf;`add_text_trace))
	`g has (`copytexttrace;(gcbf;`copy_text_trace))

Now attempt to copy the text trace on the graph (see "5f. Copying and
Deleting Trace Sets"). When the copy sequence is completed, you will
see `copy_text_trace appear in your A+ session, indicating that the
function gcbf was called, and the coordinates of the pointer at the time
the copy event occurred. The copy will not be made, naturally, since the
default meaning of the copy sequence has been superseded by the call to
gcbf.  Of course, you can redefine gcbf to put a copy of the text trace
z at the coordinates given by `coordinate of `g.

The same behavior occurs when you complete the procedure for creating a
new text trace, as described earlier in this section.

The default behavior can be restored as follows:

	`g has (`addtexttrace;)

The control of trace deletion is similar, as in: 

	`g has (`delete;(gcbf;`delete))

Now select the text trace and press Meta-Delete.

5h. Modifying and Creating Numeric Traces

It is also possible to modify numeric traces. To do this you must place
the pointer near a data point, so first zoom in on one of the clusters.
Place the pointer on a data point (i.e., a vertex of the graph) and
press and hold the right button. Small cross hairs under the pointer and
a box containing the x- and y-coordinates of the point should appear and
the connecting line segments should change color. As you move the
pointer the cross hairs will move up and down vertically, remaining
parallel with pointer. Release the button and the graph will be modified
to show the data point moved to the location of the cross hairs when the
button was released. The value of the trace set variable will have
changed accordingly.  The `selected attribute of the trace will hold the
(row index, column index) pair of the moved point.

Try modifying various points of the graph and examine the changed values
of the trace set variable.

There are two attributes associated with modifying numeric traces on the
screen. As you may have noticed, it is not necessary to place the
pointer exactly on the data point to be moved. It is only necessary to
get close to the data point, and the required closeness can be

	`g has (`selectdistance;50)

The default value for this attribute is 10, and 50 is a bit large, but
you can now see quite easily the general behavior of the data point
selection algorithm. In effect, an imaginary region based on the value
of this attribute is placed around the data point, and if the pointer
falls in that region, the data point is selected. Experiment with
selecting data points with this large value of the selectdistance

Secondly, the constraint that only the y-coordinate is modified, which is
useful for avoiding small, unwanted changes is the x-coordinates, is an
attribute value:

	`movelimit of `y
<  `x                     This is the default

If this attribute is set to `y, then only the x-coordinate can be
modified, and if it is set to `none then both coordinates can be
modified. The default is `x. Note that this attribute is effective for
two-column trace sets only; in all other trace sets, only the
y-coordinate can be modified, because either there are no explicit
x-coordinates to be modified or each x-coordinate is paired with several
y-coordinates and moving it would affect several points.

Line traces can created on the screen. Place the mouse pointer on the
graph, press and hold the Control key, and then press and hold the left
mouse button. As you move the mouse pointer a line will appear with one
end anchored at the spot where you first pressed the left mouse button,
and the other attached to the pointer. Release the mouse button and the
line segment will become fixed, with small knobs at the two ends.

You can rotate the line segment and change its length by putting the
mouse pointer on either knob, pressing and holding the left mouse
button, and moving the knob.  You can reposition it in a parallel
fashion by putting the pointer on the line away from the knobs, pressing
and holding the left mouse button, and moving the line.

You can make more line segments by putting the mouse pointer on the knob
at either end, pressing and holding the Shift key and then the left
mouse button, and then moving the pointer.  Release the mouse button to
get a new line segment. (Once the line segment connected to the pointer
appears, the Shift key can be released.)
Double-click the left mouse button to fix the line segments as a new

If at any time you change your mind about creating a new line trace,
press the Esc key. Or, if you change your mind about adding a new line
segment to a trace you are creating, but are already in the process of
doing so, move the pointer so the ends of that line segment are close
together, and release the button.

Line traces created in this way are automatically selectable, and
therefore can be moved, copied, and deleted.

As with text traces, the programmer has control over how users add,
copy, and delete line traces. For example, using the generic callback
function defined above, we can monitor the adding and copying of line

	`g has (`addtrace;(gcbf;`add_line_trace))
	`g has (`copytrace;(gcbf;`copy_line_trace))

Deleting traces is the same as for text traces. As with text traces, in
practice the callback function would be defined to carry out some action
reasonable for the application at hand.

6. Monitoring Performance

It may be necessary to improve the performance of your application by
improving its interface to graphics. Many actions cause a graph to be
completely redrawn, and some of those redrawings may be unnecessary. A
different sequence of actions may reduce the amount of redrawing, Also,
if the last point in a trace is modified only that modification should
take place on the graph, i.e., there should not be a complete redrawing.

The s.QUIET variable is a tool for monitoring performance. If it is set
to 0 (the default), then whenever the graph is redrawn, updated, or
printed, an A+ comment to that effect appears in the A+ session log.

s.QUIET can have any of four values and four corresponding sets of
messages are displayed by the screen management system:

  -1: None.

   2: Severe errors.

   1: Moderate and severe errors.

   0: Information, warnings, and moderate and severe errors.

Restricting the messages to the ones you need under the particular
execution circumstances can greatly reduce clutter in the A+ session

You have seen the information messages that are displayed. We will now
show the error messages. We start fresh.

	$off  Exit from A+

Press F4 to start A+ again, then move the cursor back to the tutorial
buffer, on the next line.

	$load s

	`g is `slot

Since g is not a slotfiller, this attempted binding is a severe error,
whose level is recognizable by the two exclamation points.

	`g is `graph
        `g has (`unknownattribute;0)

Since there is no such attribute, this attempted setting is a moderate
error, whose level is recognizable by the single exclamation point.

Back to performance.

Now we will show the graph and then set some attributes and adjust a
data point. After each action, you should see an information message,

        show `g
	`g has (`ylabelout;`float)
	`y has (`style;`scatter)

One way to reduce the number of redrawings is to set attributes before
showing the graph. For example:

	free `g
Now define g to be a graph, but do not show it:

	`g is `graph

Set the two attributes that were set above and adjust a data point

	`g has (`ylabelout;`float) 
	`y has (`style;`scatter)

Now show the graph:

	show `g

In this sequence the graph is drawn only once, while in the first
sequence it was drawn four times. This is better style as well, since
the graph will not appear to go through a series of incremental changes
to get to its final state.

Now let's leave some room to append points to y and accordingly make the
width of the graph (attribute xs) 50% larger, to accommodate the longer

	`g has (`xmax;30;  `xs;1.5  >`xs of `g)

When there is room for additional points and the append form of
assignment is used, then adding points does not cause the entire graph
to be redrawn, but only a portion, in an append operation. We will time
the first two actions, to show the efficiency of appending over
redrawing, even in a simple one-trace graph:

        time yy,98.3            Not an append assignment; redraw.
        time y[,]98.4           An append assignment; no redraw.
        y[,]98.6 98.5 98.8      Likewise.
        y[,]1298.9 98.8        Run out of space; redraw.