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<br>
Chapters:
<br>
<a href="Introduction.html">1: Introduction</a><br>
<a href="SimpleExample.html">2: Simple example</a><br>
<a href="InvokingGri.html">3: Invocation</a><br>
<a href="GettingMoreControl.html">4: Finer Control</a><br>
<a href="X-Y.html">5: X-Y Plots</a><br>
<a href="ContourPlots.html">6: Contour Plots</a><br>
<a href="Images.html">7: Image Plots</a><br>
<a href="Examples.html">8: Examples</a><br>
<a href="Commands.html">9: Gri Commands</a><br>
<a href="Programming.html">10: Programming</a><br>
<a href="Environment.html">11: Environment</a><br>
<a href="Emacs.html">12: Emacs Mode</a><br>
<a href="History.html">13: History</a><br>
<a href="Installation.html">14: Installation</a><br>
<a href="Bugs.html">15: Gri Bugs</a><br>
<a href="TestSuite.html">16: Test Suite</a><br>
<a href="GriInThePress.html">17: Gri in Press</a><br>
<a href="Acknowledgments.html">18: Acknowledgments</a><br>
<a href="License.html">19: License</a><br>
<br>
Indices:<br>
<a href="ConceptIndex.html"><i>Concepts</i></a><br>
<a href="CommandIndex.html"><i>Commands</i></a><br>
<a href="BuiltinIndex.html"><i>Variables</i></a><br>
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<h2>10.4: Variables</h2>
<UL>
<LI><a href="Variables.html#AboutVariables">About Variables</a>: What variables are used for, and how
<LI><a href="Variables.html#UserVariables">User Variables</a>: Defining your own variables
<LI><a href="Variables.html#Built-inVariables">Built-in Variables</a>: Variables pre-defined by Gri
</UL>
<!-- @node About Variables, User Variables, Variables, Variables -->
<a name="AboutVariables" ></a>
<h3>10.4.1: About variables</h3>
Variables store numbers. As it reads your program, Gri
substitutes variable values any place a variable appears where a number
normally would. For example, in the code below `<font color="#82140F"><code>.number.</code></font>' is a
variable storing the value 10, so the two `<font color="#82140F"><code>read</code></font>' statements have
the same effect:
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
.number. = 10
read columns .number. x y
read columns 10 x y
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
Variable names begin and end with a single period (example:
`<font color="#82140F"><code>.num.</code></font>'). (Gri uses this odd notation to distinguish variable
names from ``normal'' words, which is necessary because Gri does not
have a limited list of keywords as other languages do. Thus, the C
programming language is happy to let you use a variable name like
`<font color="#82140F"><code>latitude</code></font>', since it is not a keyword, but Gri is not, since it
might like to use that word itself in a new command.)
<p>
You should not use names beginning and ending with double periods,
because Gri uses names like that to store built-in variables for its own
use (e.g., `<font color="#82140F"><code>..xsize..</code></font>' saves the width of the plot).
<p>
To store a number into a variable, use a command like
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
.time. = 10
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
or
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
.time. = {rpn 10 sin}
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
Storage is automatically set aside when you assign into a nonexistent
variable; no ``declaration'' statements are required as in the C
language.
<p>
The Gri command, `<font color="82140F"><code>new</code></font>' (see <a href="New.html#New">New</a>), allows you to have several
``versions'' of a variable. This is useful for local storage in new
commands, inside `<font color="#82140F"><code>if</code></font>' statements, etc, since it lets you use
temporary variables without worrying about overwriting values outside
the local block of code. The syntax is `<font color="#82140F"><code>new .variable. = value</code></font>'
(where, as usual, `<font color="#82140F"><code>value</code></font>' may be an rpn expression
(see <a href="ReversePolishMath.html#rpnMathematics">rpn Mathematics</a>). Here is an example:
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
`foo bar'
{
new .a. # Get storage
.a. = 10 # Store a local value
show "Locally, .a.=" .a. " (expect 10)"
delete .a. # Delete this local one
}
.a. = 1
show "Global version has .a.=" .a. " (expect 1)"
foo bar
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
To see if a given named variable (or synonym) exists, use the RPN
operator `<font color="82140F"><code>defined</code></font>' (see <a href="ReversePolishMath.html#rpnMathematics">rpn Mathematics</a>).
<p>
<!-- @node User Variables, Built-in Variables, About Variables, Variables -->
<a name="UserVariables" ></a>
<h3>10.4.2: User variables</h3>
You can get Gri to read values for variables from your file. Here's how
to read a number from a header line and then read that many lines of
columnar data:
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
open file.dat
read .num.
read columns .num. x y
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
You can define variables within the Gri program:
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
.num. = 10
read columns .num. x y
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
You can get variables interactively from the user, using the
`<font color="#82140F"><code>query</code></font>' command. (If the user types carriage-return, or if the
command-line flag `<font color="#82140F"><code>-y</code></font>' was specified when invoking Gri, the value
100 will be assigned to `<font color="#82140F"><code>.num.</code></font>').
For example,
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
query .num. "Number of rows to read?" (100)
read columns .num. x y
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
Gri allows you to use a previous value of the variable in the default
string, as in this example:
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
.start. = 8 # default
.stop. = 2 # default
query .start. "Start time? " (.start.)
query .stop. "Stop time? " (.stop.)
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
Variables can be manipulated using reverse polish notation (RPN)
mathematical operations (see <a href="ReversePolishMath.html#rpnMathematics">rpn Mathematics</a>).
<p>
Variables are often useful in `<font color="#82140F"><code>if</code></font>' statements. Here are some
examples:
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
read .num_pts.
if .num_pts.
show "There are some data"
read columns .num_pts. x y
else
show "There are no data"
end if
# ...
read .latitude.
if {rpn .latitude. 10 <}
read .num.
read .num. x y
draw curve
else
show "Skipping data North of 10deg N"
read .num.
skip .num.
end if
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<!-- @node Built-in Variables, Synonyms, User Variables, Variables -->
<a name="Built-inVariables" ></a>
<h3>10.4.3: Built-in variables</h3>
Built-in variables (see <a href="BuiltinIndex.html#IndexofBuiltins">Index of Builtins</a>) have names which begin and
end with <b>two</b> periods. For example, `<font color="#82140F"><code>..xsize..</code></font>' is the width
of the x-axis in centimetres. You may use these variables as you wish
(example: `<font color="#82140F"><code>..xsize.. = 4</code></font>' is an alternative to
`<font color="#82140F"><code>set x size 4</code></font>'), but you must be aware that these are not ``free''
variables for you to use for arbitrary purposes. You can find out what
the built-in variables are by the command `<font color="#82140F"><code>show variables</code></font>'.
<p>
There are two types of variables
<ul>
<li>
<b>Startup</b> variables, which are created by Gri at startup time.
These variables can be relied upon to exist (barring changes in Gri
itself), unless you `<font color="#82140F"><code>delete</code></font>' them.
<li>
<b>Spontaneous</b> variables (which are created by certain Gri commands,
and only exist if these commands have been executed). For example, the
`<font color="#82140F"><code>regress</code></font>' command defines `<font color="#82140F"><code>..coeff0..</code></font>' (the intercept of the
fitted line), `<font color="#82140F"><code>..coeff1..</code></font>' (the slope of the fitted line),
`<font color="#82140F"><code>..R2..</code></font>' (the correlation coefficient).
</ul>
<p>
To see the values of the built-in variables (along with the user
variables), use `<font color="#82140F"><code>show variables</code></font>'. Here are some useful builtin
variables:
<p>
<ul>
<p>
<li> `<font color="#82140F"><code>..arrowsize..</code></font>'
<!-- latex: \index{@code{..arrowsize..}, size of arrows} -->
Stores either a positive number representing the halfwidth of arrowheads
measured in centimetres, or a negative number giving the negative of the
ratio of arrowhead halfwidth to arrow length (see <a href="Set.html#SetArrowSize">Set Arrow Size</a>).
<p>
<li> `<font color="#82140F"><code>..batch..</code></font>'
<!-- latex: \index{@code{..batch..}, flag used for batch mode} -->
Flag used for batch mode.
<p>
<li> `<font color="#82140F"><code>..debug..</code></font>'
<!-- latex: \index{@code{..debug..}, flag used for debugging} -->
Equal to 1 if the `<font color="#82140F"><code>-debug</code></font>' command-line flag was set. Flag used
for debugging (see <a href="InvokingGri.html#InvokingGri">Invoking Gri</a>). The `<font color="82140F"><code>..debug..</code></font>'
built-in variable is useful in isolating code to use only in test runs.
For example, you might use
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
if ..debug..
show "Following are the column data"
show columns
end if
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
When you run the program with command-line `<font color="#82140F"><code>gri -debug file.gri</code></font>'
the code in the `<font color="#82140F"><code>if</code></font>' block will print out the columnar data, but
when you run it with `<font color="#82140F"><code>gri file.gri</code></font>' these lines are not printed.
<p>
<li> `<font color="#82140F"><code>..eof..</code></font>'
<!-- latex: \index{@code{..eof..}, flag indicating end-of-file} -->
Flag indicating whether an end-of-file was encountered on the last
`<font color="#82140F"><code>read columns</code></font>'.
<p>
<li> `<font color="#82140F"><code>..words_in_dataline..</code></font>'
<!-- latex: \index{@code{..words_in_dataline..}} -->
Number of words on last dataline. This is useful in constructs like
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
open tmp.dat
.num. = 0
while 1
read .a. .b.
if !..words_in_dataline..
show "Got empty line or EOF, so break loop"
break
end if
show "a=" .a. "b=" .b.
show "; words in line=" ..words_in_dataline..
.num. += 1
end while
show "Got " .num. "data lines."
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<li> `<font color="#82140F"><code>..fontsize..</code></font>'
<!-- latex: \index{@code{..fontsize..}, size of letters} -->
Size of letters, measured in points; there are 72.27 points in an inch
and 28.45 points in a centimetre. The mathematical operators
`<font color="#82140F"><code>pttocm</code></font>' and `<font color="#82140F"><code>cmtopt</code></font>', which do conversion between points and
centimetres, are often useful in labelling data curves
(see <a href="ReversePolishMath.html#rpnMathematics">rpn Mathematics</a>).
<p>
<li> `<font color="#82140F"><code>..graylevel..</code></font>'
<!-- latex: \index{@code{..graylevel..}, graylevel (0=black)} -->
Graylevel to use in drawing lines, text, etc. Black ink is 0; white
paper is 1. <b>See also</b> `<font color="#82140F"><code>..red..</code></font>' etc.
<p>
<li> `<font color="#82140F"><code>..image_height..</code></font>'
<!-- latex: \index{@code{..image_height..}, height of image} -->
Height of image, or 0 if no image defined yet.
<p>
<li> `<font color="#82140F"><code>..image_width..</code></font>'
<!-- latex: \index{@code{..image_width..}, width of image} -->
Width of image, or 0 if no image defined yet.
<p>
<li> `<font color="#82140F"><code>..length_dash..</code></font>'
<!-- latex: \index{@code{..length_dash..}, length/cm of dashes} -->
Length in cm of dashes in dashed lines.
<p>
<li> `<font color="#82140F"><code>..length_blank..</code></font>'
<!-- latex: \index{@code{..length_blank..}, length/cm of blanks} -->
Length in cm of blanks in dashed lines.
<p>
<li> `<font color="#82140F"><code>..linewidth..</code></font>'
<!-- latex: \index{@code{..linewidth..}, width of lines} -->
Width of lines for data curves (see <a href="Set.html#SetLineWidth">Set Line Width</a>).
<p>
<li> `<font color="#82140F"><code>..linewidthaxis..</code></font>'
<!-- latex: \index{@code{..linewidthaxis..}, width of lines on axis} -->
Width of lines on axes (see <a href="Set.html#SetLineWidth">Set Line Width</a>).
<p>
<li> `<font color="#82140F"><code>..linewidthsymbol..</code></font>'
<!-- latex: \index{@code{..linewidthsymbol..}, width of lines in symbols} -->
Width of lines in symbols (see <a href="Set.html#SetLineWidth">Set Line Width</a>).
<p>
<li> `<font color="#82140F"><code>..missingvalue..</code></font>'
<!-- latex: \index{@code{..missingvalue..}, missing value code} -->
Missing value code, also stored in the synonym `<font color="#82140F"><code>\.missingvalue.</code></font>';
(see <a href="Set.html#SetMissingValue">Set Missing Value</a>).
<p>
<li> `<font color="#82140F"><code>..num_col_data..</code></font>'
<!-- latex: \index{@code{..num_col_data..}, number column data} -->
Number of column data that exist. You might want to use this after
`<font color="#82140F"><code>read columns</code></font>' to see if a data file actually had any data in it,
or use it in accessing individual elements of columns
(see <a href="ReversePolishMath.html#rpnMathematics">rpn Mathematics</a>).
<p>
<li> `<font color="#82140F"><code>..publication..</code></font>'
<!-- latex: \index{@code{..publication..}, flag for final copy of plot} -->
Flag for final copy of plot. The command-line option `<font color="#82140F"><code>-p</code></font>' sets the
value of `<font color="#82140F"><code>..publication..</code></font>' to 1. A typical, and highly
recommended, code fragment is
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
if !..publication..
draw time stamp
end if
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<li> `<font color="#82140F"><code>..red..</code></font>', `<font color="#82140F"><code>..green..</code></font>', `<font color="#82140F"><code>..blue..</code></font>'
<!-- latex: \index{@code{..blue..}} -->
Description of present color. The values are between 0 and 1, with
(0,0,0) being black and (1,1,1) being white. If color is gray, all
these will be equal. You may assign to these, but it will <b>not</b>
change the color.
<p>
<li> `<font color="#82140F"><code>..symbolsize..</code></font>'
<!-- latex: \index{@code{..symbolsize..}, size of symbols} -->
Size of symbols in centimetres.
<p>
<li> `<font color="#82140F"><code>..superuser..</code></font>'
<!-- latex: \index{@code{..superuser..}, was -superuser flag set?} -->
Equal to 0 if the flag was not set, or equal to the flag if it was.
<p>
<li> `<font color="#82140F"><code>..tic_direction..</code></font>'
<!-- latex: \index{@code{..tic_direction..}, direction of axis tics} -->
Direction of axis tics, 1 for inside or 0 for outside.
<p>
<li> `<font color="#82140F"><code>..tic_size..</code></font>'
<!-- latex: \index{@code{..tic_size..}, size/cm of axis tics} -->
Size of axis tics in centimetres.
<p>
<li> `<font color="#82140F"><code>..trace..</code></font>'
<!-- latex: \index{@code{..trace..}, for tracing program execution} -->
Equal to 1 if the `<font color="#82140F"><code>-trace</code></font>' command-line flag was set. Used for
tracing program execution.
<p>
<li> `<font color="#82140F"><code>..xinc..</code></font>'
<!-- latex: \index{@code{..xinc..}, x increment on axes} -->
x increment on axes.
<p>
<li> `<font color="#82140F"><code>..xleft..</code></font>'
<!-- latex: \index{@code{..xleft..}, x value at left of plot} -->
x value at left of plot.
<p>
<li> `<font color="#82140F"><code>..xmargin..</code></font>'
<!-- latex: \index{@code{..xmargin..}, left margin} -->
Left margin, in centimetres.
<p>
<li> `<font color="#82140F"><code>..xright..</code></font>'
<!-- latex: \index{@code{..xright..}, x value at right of plot} -->
x value at right of plot.
<p>
<li> `<font color="#82140F"><code>..xsize..</code></font>'
<!-- latex: \index{@code{..xsize..}, x-axis length} -->
x-axis length in centimetres.
<p>
<li> `<font color="#82140F"><code>..ybottom..</code></font>'
<!-- latex: \index{@code{..ybottom..}, y value at bottom of plot} -->
y value at bottom of plot.
<p>
<li> `<font color="#82140F"><code>..yinc..</code></font>'
<!-- latex: \index{@code{..yinc..}, y increment on axes} -->
y increment on axes.
<p>
<li> `<font color="#82140F"><code>..ymargin..</code></font>'
<!-- latex: \index{@code{..ymargin..}, bottom margin} -->
Bottom margin in centimetres.
<p>
<li> `<font color="#82140F"><code>..ysize..</code></font>'
<!-- latex: \index{@code{..ysize..}, y-axis length} -->
y-axis length in centimetres.
<p>
<li> `<font color="#82140F"><code>..ytop..</code></font>'
<!-- latex: \index{@code{..ytop..}, y value at top of plot} -->
y value at top of plot
<p>
<li> `<font color="#82140F"><code>..exit_status..</code></font>'
<!-- latex: \index{@code{..exit_status..}, exit status from @code{system} call} -->
The exit status from the most recent `<font color="#82140F"><code>system</code></font>' call (or 0 if no
system calls have been done yet).
</ul>
<p>
You may use any of these built-in variables anywhere. For example,
here's how to stack 3 graphs vertically on the page:
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
.offset. = {rpn ..ysize.. 3 + }
open file1
read columns x y
close
draw axes
draw curve
<p>
..ymargin.. += .offset.
open file2
read columns x y
draw axes
draw curve
close
<p>
..ymargin.. += .offset.
open file3
read columns x y
draw axes
draw curve
close
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
The first line needs a bit of explanation. It is a reverse-polish
expression. The format is `<font color="#82140F"><code>{</code></font>' followed by `<font color="#82140F"><code>rpn</code></font>' followed by
an expression followed by `<font color="#82140F"><code>}</code></font>'. Within the expression, spaces must
separate operands. This makes `<font color="#82140F"><code>.offset.</code></font>' equal to the height of
y-axis plus 3 cm, so plots are separated by 3 cm. To learn more about
`<font color="82140F"><code>{rpn ... }</code></font>' (see <a href="ReversePolishMath.html#rpnMathematics">rpn Mathematics</a>).
<p>
Another possibly unfamiliar thing is the code `<font color="#82140F"><code>+=</code></font>'. It means take
the thing on the left hand side, and add to it the thing on the right
hand side. (In this case, it is used to increase the y margin by the
value of `<font color="#82140F"><code>.offset.</code></font>'.)
<p>
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