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<title>Gri: introduction</title>
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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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<h1>1: Introduction</h1>
<b>Gri is a programming language for drawing science-style graphs</b>.
It is not mouse-driven, and it does not draw business-style graphs
(e.g. pie charts, three-dimensional graphs). Gri has substantial power
in advanced applications. It has been proven to be easy to learn; for
simple applications, the learning curve is less than an hour. Many
users regard Gri as the plotting equivalent of the LaTeX document
preparation system.
<p>
<b>Computers Gri works on:</b> unix computers of many types, plus
Microsoft Windows, and Macintosh OSX. You'll find Gri pre-packaged
for various unixes, e.g. linux/debian, linux/redhat, and freeBSD.
<p>
<b>Capabilities of Gri</b> are those scientists commonly want, since Gri
was written by a scientist. It is not so useful for business people --
e.g., Gri draws xy graphs (see <a href="X-Y.html#X-yPlots">X-y Plots</a>), contour plots
(see <a href="ContourPlots.html#ContourPlots">Contour Plots</a>), and image plots
(see <a href="Images.html#Images">Images</a>), but it will
not draw pie-charts unless you teach it how. The list of capabilities
of Gri is similar to many packages, but unlike many of the other
packages, Gri gives you control over line widths, fonts, grayscales,
etc. (see <a href="GettingMoreControl.html#GettingMoreControl">Getting More Control</a>), and it is a programming language
of moderate power.
<p>
<b>The Gri drawing metaphor</b> is that of pen on paper. The ink in the
pen is opaque. An item drawn in white ink will erase a previously drawn
underlying object drawn in black ink. For example, to draw a timeseries
curve in which the region between positive data values and the y=0 axis
is filled with black ink, you might use (`<font color="#82140F"><code>draw curve filled</code></font>') to
draw the timeseries with black ink (the default color), blackening the
area between the curve and the lower axis. Then you could load white
ink into the pen (using the `<font color="#82140F"><code>set graylevel 1</code></font>' or
`<font color="#82140F"><code>set graylevel white</code></font>' command) and white-out a box drawn between the zero
line and the lower axis. Then you'd load black ink back into the pen
(`<font color="#82140F"><code>set graylevel 0</code></font>') and draw the curve again, so that the negative
part would appear again.
<p>
<b>Input/output</b> in Gri may be interactive or non-interactive. For
interactive use, type `<font color="#82140F"><code>gri</code></font>' at the system commandline prompt. For
non-interactive use, with Gri commands in a command-file called
`<font color="#82140F"><samp>cmd.gri</samp></font>', type `<font color="#82140F"><code>gri cmd.gri</code></font>'.
<p>
<b>Gri output</b> is in the PostScript page description language. The
output is therefore of high quality, device-independent, capable of
being inserted into popular text processors (e.g. LaTeX), and easily
displayed.
<p>
<b>Online help:</b> the Gri command `<font color="#82140F"><code>help</code></font>' makes Gri
list the first words of all known commands, along with a hint for
getting further help. To get more information, type `<font color="#82140F"><code>help</code></font>'
followed by a command-name (e.g. `<font color="#82140F"><code>help read</code></font>'). There is also a
tiny bit of information stored online and categorized by topic. Get
this by typing for example `<font color="82140F"><code>help - strings</code></font>' (see <a href="OnlineHelp.html#OnlineHelp">Online Help</a>).
<p>
<b>Data analysis</b> in Gri is limited. It has rudimentary data
analysis functions, such as regression, column manipulation, smoothing,
etc, but it is not intended as an integrated analysis/graphics package.
<p>
<b>System calls</b> are an easy and important facet of Gri. It is easy
to use operating system commands within Gri (see <a href="System.html#System">System</a>;
see <a href="OperatingSystem.html#OperatingSystem">Operating System</a>;
see <a href="GetEnv.html#GetEnv">Get Env</a>). This
allows you to use familiar, powerful tools, and keeps Gri simple.
Particularly useful is the ability to read files through operating
system filters (see <a href="Open.html#Open">Open</a>).
<p>
<b>Programming Gri</b> is quite straightforward, and users familiar with
other programming languages find it easy. If Gri lacks a drawing
method, you can add it fairly easily, since Gri has programming elements
such as `<font color="82140F"><code>if</code></font>' statements (see <a href="IfStatements.html#IfStatements">If Statements</a>), `<font color="#82140F"><code>while</code></font>' loops
(see <a href="While.html#While">While</a>), facilities for interacting with the user
(see <a href="Query.html#Query">Query</a>), and mechanisms for storing numbers in "variables"
(see <a href="Variables.html#Variables">Variables</a>),
and text strings in "synonyms" (see <a href="Synonyms.html#Synonyms">Synonyms</a>). The Gri syntax can
be augmented easily (see <a href="NewCommands.html#AddingNewCommands">Adding New Commands</a>), and these
augmentations can be stored in a startup file (see <a href="ResourceFile.html#ResourceFile">Resource File</a>),
creating personalized versions of Gri.
<p>
<b>Manuals:</b> Gri has an online texinfo manual, a PostScript manual, a
WWW manual, a
<A HREF="http://gri.sourceforge.net/gri-cookbook/index.html">
cookbook
</A>
and several reference cards. It also has several discussion groups
(see <a href="DiscussionGroup.html#DiscussionGroup">Discussion Group</a>).
<p>
<b>Version Numbering Scheme</b>
<p>
When you launch Gri interactively (without naming a commandfile, i.e. by
just typing `<font color="#82140F"><code>gri</code></font>' at the unix prompt), you'll see something like
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
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<TD>
<PRE>
<font color="#82140F">
gri - scientific graphic program (version 2.12.26)
GPL Copyright 2015 by Dan E. Kelley.
<p>
Type `help' for an overview of Gri commands, or see the
full manual at
/usr/share/doc/gri-2.12.26/html/index.html
and its text-only version in the 'gri' INFO node.
<p>
Visit http://gri.sourceforge.net for updates and resources.
gri:
</font></PRE>
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</TABLE>
<p>
The last line is a prompt, suggesting that you type in Gri commands.
You may type `<font color="#82140F"><code>quit</code></font>' to get out of gri.
<p>
The first line gives the version number. You can also get this by
running Gri with the command `<font color="#82140F"><code>gri -v</code></font>'. Version numbers have three
numbers separated by periods. The first number increments for major
changes, the second for smaller changes, the third for still smaller
changes. The second number also indicates whether a copy is an
experimental version or a more reliable release version. Experimental
versions have the second digit being an odd integer, while release
versions have this digit being even.
<p>
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