Introduction

This is the FAQ ("frequently asked questions") document for the Gri scientific graphing language, (c) 1991-1999 Dan Kelley (Dan.Kelley@Dal.Ca), to whom you are asked to email reports of Gri errors, or suggestions for Gri improvements or new features.

The Questions

Q1 Features

Q2 Documentation

Q3 Can Gri do ... ?

Q4 Gri and other programs

Q5 Evolution of Gri

Q6 Gri on various computers

Q7 Gri bugs

The Answers


A1 Features

A1.1 What is Gri?

Gri is a program for drawing scientific graphs. It makes xy plots (linegraphs and scattergraphs), contour plots, and image plots. Unlike many scientific plotting packages, Gri provides precise control over fonts, line widths, grayscales, colors, etc. Since Gri was written by a scientist, it does the kinds of plots scientists want. It has few frills; e.g., it does not do 3D mesh plots, because the author dislikes them. Gri is command-driven, not mouse driven.

A1.2 What does `Gri' stand for? How is it pronounced?

Gri stands for `gr-interactive', and `gr' is the name of a subroutine library that preceded Gri. The `interactive' adjective indicates that Gri can be used interactively -- that is, Gri is an interpreted language whereas Gr is a compiled language. `Gri' rhymes with `try'.

A1.3 What does Gri cost?

Gri is free. A commercial version, called Gre (rhymes with `tree') will be made available in 1999. It contains most of Gri as a subset, but also contains quite a lot of the Perl language as well, making it a fully functional and efficient programming language.

A1.4 How long will it take to learn Gri?

Most users can get Gri working after spending half an hour with manual (see Q2.1). Familiarity with your operating system (for example for viewing PostScript files) will speed this somewhat. After that, it's best to learn new features only as you come to need them. To begin with, you should skim the manual and the cookbook (see Q2.3), looking just at the illustrations. This will take no more than an hour.

The Gri manual is like most computer manuals: it would be a waste of time to read it cover to cover before starting to use Gri. But you'll find the manual helpful as you branch out, modifying the existing examples and inventing code of your own.

Learning how to use a new command usually takes only a minute but realizing that the command exists can take longer. That's why many users with sophisticated needs find it useful to spend an afternoon leafing through the entire manual at some point.

Most things in Gri can be done elegantly or crudely. The elegant approach may require a little investment in time at the beginning, but this will pay off constantly as your needs grow. For example, folks who like computer programming often start using Gri "newcommands" (a form of subroutines) within a few days. Other folks might avoid newcommands, instead putting their entire program in one long "main routine". What's right for you depends on how you think and the sort of work you do.


A2 Documentation

A2.1 Is there a quick-reference card for Gri?

Yes, two quick-reference cards are stored on the FTP site ftp://ftp.phys.ocean.dal.ca/users/kelley/gri (the base address is 129.173.3.50). The PostScript file refcard.ps is an overview of Gri syntax and usage, while cmdrefcard.ps is a full list of Gri commands. Each of these files is also available in TeX format.

A2.2 Where can I get documentation for Gri?

Full documentation is available in several forms on the FTP site FTP site ftp://ftp.phys.ocean.dal.ca/users/kelley/gri (the base address is 129.173.3.50). Check out the FAQ file (which you are reading now), cmdrefcard.ps (a PostScript reference card listing all Gri commands), refcard.ps (a PostScript reference card overviewing Gri), and a file called something like gri_manual_2.051.tar.gz (which is a complete PostScript manual including figures). To save time and paper, you should look at the FAQ and the two reference cards first.

The Gri manual is available on the WWW (world wide web) at the URL http://www.phys.ocean.dal.ca/~kelley/gri/gri1.html . A searchable index is available there, which is very useful.

A2.3 Is there a cookbook of Gri programs to use for guidance?

Yes, at the website http://www.phys.ocean.dal.ca/~kelley/gri/cookbook/cookbook.html

A2.4 Is there a newsgroup for Gri?

No, but there is a mail-list type newsgroup. The group is maintained automatically by a program called majordomo. Operations like getting on or off the list are done by mailing to majordomo@phys.ocean.dal.ca; to subscribe, send a message containing just the two words subscribe gri, and to unsubscribe send the words unsubscribe gri. You can also send the message help to find out other usefull majordomo commands.

To see what messages have been posted to the group, send a message to majordomo@phys.ocean.dal.ca containing the line send gri gri.archive.

Mailing to the list -- that is, to other Gri users -- is different. Then you mail to gri@phys.ocean.dal.ca. There is not very much traffic on the list, but please use it responsibly because everything you send will be mailed to dozens of other folks who are just as busy as you are. In particular please do not mail any requests intended for majordomo to the Gri list.

A2.5 Where can I get some sample Gri input files?

You can get them from the anonymous FTP site ftp://ftp.phys.ocean.dal.ca/users/kelley/gri (the base address is 129.173.3.50). It is in the compressed tarfile with the word 'example' contained in it. The file is compressed with the program "gzip," so you'll type

	gunzip gri-examples-2.1.10.tar.gz
	tar xvf  gri-examples-2.1.10.tar
(where 2.1.10 will be changed to the current version number), and the tar program will create a directory called 'examples' which contains the example .gri programs and datafiles. The 'examples' directory also contains subdirectories with names that reflect computer names (e.g., SGI, SUN4). To get run gri on all the examples, go into the appropriate subdirectory and type 'make examples'. For example:
	cd examples/SUN4
	make examples
creates files examples/SUN4/example1.ps, examples/SUN4/example2.ps, etc.

A3 Can Gri do ... ?

A3.1 Can Gri do barcharts?

Gri has no specific command for barcharts, but the operating system can easily rearrange your data into a form that lets Gri draw barcharts. In the following example, the synonym \width is set to the desired width of the bars and \missing is set to an arbitrary missing value. The rest of the code will make sense to any Perl programmer. If you don't know Perl, you should learn it.

\width = "1"                    // width of bars, in x units
\missing = "-99"                // missing value
set missing value \missing
set x axis 0 6 1
set y axis 0 20 10 
draw axes none                  // will get whited out by the chart anyway

// Create dataset
system cat > barchart.dat << "EOF"
1 12
2 14
3 15
4 13
5 10
EOF

// Create barchart style dataset and plot it
system perl <<"EOF"
open (IN, "barchart.dat") || die "Cannot open barchart.dat";
while(<IN>) {
    ($x[$i], $y[$i]) = split(' ');
    $i++;
}
$n = $i;
open (TMP, ">tmp") || die "Cannot open tmp";
for ($i = 0; $i < $n; $i++) {
    print TMP $x[$i] - \width / 2, " ",      0, "\n";
    print TMP $x[$i] - \width / 2, " ", $y[$i], "\n";
    print TMP $x[$i] + \width / 2, " ", $y[$i], "\n";
    print TMP $x[$i] + \width / 2, " ",      0, "\n";
    print TMP \missing, " ", \missing, "\n";
}
EOF
open tmp
read columns x y
set graylevel 0.95
draw curve filled to 0 y
set graylevel 0
draw curve
draw axes
draw title "Demonstrate Gri barchart"

A3.2 Can Gri do histograms?

Gri has no specific command for histograms, but the operating system can easily rearrange your data into a histogram format.

Here is Gri code to do it:

open "histogram -l 0 -h 10 -i 0.5 < inputfile |"
read columns x y // y is number of obs
draw curve filled to 0 y

where histogram is a perlscript which creates a histogram file named inputfile. An example of histogram is:

#!/opt/bin/perl
# Calculate histogram of 1-column data
$usage ="\
NAME\
     histogram -- create histogram file, given data file (1 column)\
\
SYNOPSIS\
     histogram -l low -h high -i increment < input_file > output_file\
\
DESCRIPTION\
     Scans the input values and finds the percentage of data in bins\
     starting at value `low', ending at value `high', and incrementing by\
     value `inc'.\
\
FILES\
     Standard input:  column of numbers\
     Standard output: columns: (bin_centre, per, cum_per, num, cum_num)\
         where 'per'=percentage and 'num'=number.\
";
require "getopts.pl";
$opt_l = 0;
$opt_h = 0;
$opt_i = 0;
&Getopts('l:h:i:');
die "You must supply commandline arguments!\n$usage" if ($opt_l == $opt_h || $opt_i == 0);
$n = ($opt_h - $opt_l) / $opt_i;
print STDERR "Will have $n bins, running from $opt_l to $opt_h in steps of $opt_i\n";
for ($i = 0; $i <= $n; $i++) {
    $bin[$i] = 0;
}
while(<>) {
    chop;
    ($x) = split;
    $i = int(0.5 + ($x - $opt_l) / $opt_i);
    $i =  0 if ($i < 0);
    $i = $n if ($i > $n);
    $bin[$i]++;
}
for ($i = 0; $i <= $n; $i++) {
    $x = $opt_l + $opt_i * ($i - 0.5);
    print "$x $bin[$i]\n";
    $x = $opt_l + $opt_i * ($i + 0.5);
    print "$x $bin[$i]\n";
}

A3.3 Can Gri do error bars?

Gri has no specific command for error bars. It has no internal representation of error bar data -- that is, you can't get them by a read columns command. However, you can get error bars quite easily, simply by reading the data line by line, plotting each one as individually. Here's an example of error bars in y, where the third column stores the error:

open a.dat
while 1
    read .x. .y. .ey.
    if ..eof..
        break
    end if
    draw symbol bullet at .x. .y.
    draw line from .x. {rpn .y. .ey. -} to .x. {rpn .y. .ey. +}
end while

A3.4 Can Gri draw labels for Tukey box plots?

Yes. Here is sample code, in which a label "My Label" is drawn to the right of the median of a Tukey plot extending in the y direction:

read columns x y
1 11
2 22
1.2 3
3 5
2 20
3 10

draw y box plot at 2
draw label "My Label" at {rpn 2 xusertocm 0.4 +} \
    {rpn y median yusertocm "M" ascent 2 / -} \
    cm

A3.5 Can Gri read compressed data files?

Gri has no specific way to read compressed data files, but it is trivial to trick it to do so, by using the unix-style piped open command, as in this example:

open "zcat compressed_file.Z |"
// do any normal 'read' commands 
Naturally, this works for files that have been compressed with the GNU compressor also, so long as you have the uncompressing software installed on your system.

A3.6 Can Gri use scientific notation on axes?

You have to trick it. Here's an example:

// NOTE: this requires manual setting of axes.
read columns x y
1 1.1e3
2 1.0e3
3 1.4e3
4 2.3e3
4 1.0e4

y /= 1e3
set y axis 1 5 1
set y format "%g$\times10^3$"
draw curve

A3.7 Can Gri label x-axis with day of week?

A future version of Gri will have much more powerful and general ways of handling axes labelling. In the meantime, you have to trick Gri to get such special effects. Here's an example:

set x axis 1 8 1
set y axis 0 1 .1
set font size 0
draw x axis at top
draw y axis at right
draw x axis at bottom
set font size 12
draw y axis at left
draw label "Mon" centered at 1.5 {rpn ..ymargin.. 0.7 - ycmtouser}
draw label "Tue" centered at 2.5 {rpn ..ymargin.. 0.7 - ycmtouser}
draw label "Wed" centered at 3.5 {rpn ..ymargin.. 0.7 - ycmtouser}
draw label "Thu" centered at 4.5 {rpn ..ymargin.. 0.7 - ycmtouser}
draw label "Fri" centered at 5.5 {rpn ..ymargin.. 0.7 - ycmtouser}
draw label "Sat" centered at 6.5 {rpn ..ymargin.. 0.7 - ycmtouser}
draw label "Sun" centered at 7.5 {rpn ..ymargin.. 0.7 - ycmtouser}
Note that the offset of 0.7 centimeters looks OK to me, with a 12 point font, but you may wish to experiment if you don't like the placement.

A3.8 Can Gri draw maps?

Gri can draw maps, but it lacks builtin support for map projections. (A previous version had projections, but they were not working correctly and were removed.) Gri does not have builtin coastline files, either. Many good coastline files are on the web; see, for example, Rich Signell's site http://crusty.er.usgs.gov/coast/getcoast.html or the USGS mapping site http://www.usgs.gov or the Global Self-consistent Hierarchical High-resolution Shoreline site http://www.ngdc.noaa.gov/mgg/shorelines/gshhs.html


A4 Gri and other programs

A4.1 Is Gri better than Fortran/C/... plotting subroutines?

Gri started out as a set of subroutines. The set is called `gr'; the name `gri' means gr-interactive. Although I wrote both `gr' and `gri', I haven't used gr in years. I am unaware of anybody else who ever used `gr'. Thus, in at least this case, the interpreted Gri language is superior to subroutines.

In some applications the graphics are hard-wired into the computation so using Gri might not make sense. An example is the SPEM numerical model, which has builtin NCAR plotting calls. But this approach is inefficient in user-time and computer-time, because changing the format of the output may require re-running a model. The best approach is to decouple preparation of data from presentation of data.

In highly interactive applications, such as many uses of matlab and statistical programs such as S and S-plus, it may make sense to use the builtin graphics routines because they are so tightly bound to the processing.

A4.2 How can I include Gri plots in LaTeX files?

This is done outside LaTeX (or TeX), with the program that converts from DVI format to PostScript format. This conversion is done differently on different computers; you'll have to enquire locally. With `dvips', you can use the `\special' command or the `\espfbox' command. The epsfbox command is smarter, since it figures the plot dimensions from the PostScript file itself. Unfortunately, old versions of Gri do not insert the correct plot dimensions in the PostScript file. Here's an example, for a 15cm tall figure, of how to insert a Gri PostScript file into a figure:

\documentstyle{article}
\begin{document}

... Figure \ref{fig1} shows ...

\begin{figure}
\vspace*{15cm}			% MAKE ENOUGH SPACE
\special{psfile=fig1.ps}	% THIS INSERTS THE PLOT
\caption[Short caption, which appears in list of figures.]
{\label{fig1} Long caption, which appears with the figure.}
\end{figure}

\end{document}
In other LaTeX and TeX dialects, of course (e.g. the lovely agu++ format), you'll do things differently; the above will give you enough of a guide.

A4.3 How may I convert Gri output to GIF format?

Conversion of the Gri PostScript output to GIF is normally done for inclusion in web-pages. For a discussion of the merits of various image formats, see Information Architecture. I have been told that GIF images suffer from both technical limitations (no gamma value is stored in the file) and license restrictions. The PNG format was designed to overcome these limitations, and is expected to replace GIF before the year 2000.

It should also be noted that there is no generally acceptable way to convert PostScript to gif, especially when the PostScript is vector based. One problem is that of resolution: if the output GIF is low-resolution, then the text may be drawn roughly because of rasterization. In many convertors one may specify the size of the output image, which permits control over this resolution problem, giving the user the task of weighing file size against output quality. Note also that the colour table frequently gets reordered in the conversion, possibly leading to inaccurate results. Simply stated, PostScript is superior to GIF and other raster-based formats. That's why Gri chose PostScript for the output model.

There are several ways to convert Gri PostScript into GIF images.

Availability of software: ImageMagick uses Aladdin Ghostscript, another free program, to rasterize the PostScript file created by gri. Ghostscript is available from http://www.cs.wisc.edu/~ghost/index.html and many other sites (including any CTAN archive). Older version of ghostscript are available under the GNU GPL. Speaking of GNU, gs and other GNU software are freely available at many locations on the web, e.g. ftp://prep.ai.mit.edu/pub/gnu .

Author's note: this answer was compiled with advice from Peter Galbraith, Toru Suzuki, and George White, to each of whom I am very grateful for the help. In fact, the answer is mostly a patchwork of their suggestions, and all the helpful pointers to information on the web are theirs, not mine.

A4.4 Is there an Emacs mode for Gri?

Yes. Peter Galbraith has written a very powerful mode for Gri commandfiles. Available on anonymous FTP at the site ftp.phys.ocean.dal.ca in users/rhogee . See the files gri-mode.el and gri-mode.readme. The capabilities include:


A5 Evolution of Gri

A5.1 Where can I get the latest version of Gri?

To get Gri, you use anonymous FTP to the site site ftp.phys.ocean.dal.ca or 129.173.3.50. (Use 'anonymous' as the username and your normal username as the password.) Next, go to the Gri directory:
        cd users/kelley/gri
and get the instruction files:
        mget README.*

These files tell you what to do next. If you are not familiar with such things, you might want to exit from FTP and read the README files. Otherwise, just do a directory listing and pick up the item you want. For example, to get the Sun binary version, get the file with the word ``Sun'' in it:

        binary
        get gri-binary-SunOS5-2.1.10.tar.gz
and then type
        quit
to get out of FTP, and
        zcat gri-binary-SunOS5-2.1.10.tar.gz | gar xvf -
to decode the contents.

A5.2 How can I find out the most recent features of Gri?

Do anonymous ftp to phys.ocean.dal.ca (129.173.3.50) and cd to the directory /users/kelley/gri. Pick up the file ChangeLog. For more details, see the chapter called "History" in the manual.

A5.3 Should I keep my copy of Gri up-to-date?

The advantages of being up-do-date are:

Most people should not be more than 5-10 versions out of date. To keep in touch, subscribe to the gri maillist (...see Q2.3). Also, keep track of the file ChangeLog in the FTP location. As with most software, the supplier may be more enthusiastic about new versions than the users are. Other Gri users may therefore provide the best advice on whether it is worth upgrading.

Every time you get a new copy of Gri, you should get a new online manual, and you should get/print the command reference card from the FTP site ftp://ftp.phys.ocean.dal.ca/users/kelley/gri (the base address is 129.173.3.50).

A5.4 How can I protect myself against changes to Gri?

Do three things:


A6 Gri on various computers

A6.1 What computers does Gri work on?

Gri has been ported to several Unix machines (e.g. Sun solaris and sunOS; IBM RISC; HP RISC; SGI; DEC alpha; and x86 linux) and to x86 MS-DOS. An old version is available for DEC vax VMS.

A6.2 What kind of compiler is required to compile gri?

Gri requires a C++ compiler capable of handling the language feature called "templates," and it also needs the so-called "standard template library" (STL). Templates have been a feature of C++ since about 1994, and STL became part of the draft C++ library standard in early 1996. If your compiler vendor does not support templates or STL, you should obtain a newer compiler.

The free C++ compiler called g++, available from the Free Software Foundation, is known to compile Gri on at least a half-dozen problems. The compiler version must be 2.7.2 or higher for success.

A6.3 Why can't I link my compiled gri? (on HP computer)

Unfortunately, I made a bad programming decision several versions ago -- I decided to start using the STL (the standard template library). The STL is part of the draft ANSI C++ standard, so I figured I'd be safe. And my tests on solaris and linux platforms indicated that STL worked as advertised, in g++ 2.7.x. However, I should have checked further. It turns out that g++ on some platforms (e.g. HP's unix and IBMRS's AIX unix) does not handle templates properly. The linker cannot locate templates defined in one file and used in another. This issue is discussed at some length in the g++ documentation, where three methods are presented for solving the problem. (In the info-format documentation, you can find the relevant parts by searching for the string "where's the template?") In Gri I've used what method 3 as defined in the g++ manual. Apparently this fails on some platforms. Although I'd welcome tests by users on the other two g++ methods, and I'd be happy to switch if one of them appeared to work more universally, I have to say that I'm not optimistic: from what I read on the newsgroups, nobody is having much success on this. The GNU folks say that g++ version 2.8 will handle templates much better, so I'm waiting for that. Unfortunately it's been, so far, a two-year wait.

Almost certainly, commercial compilers handle templates better, but I lack resources to purchase these for the various platforms. I'd be happy, though, to act as a broker for anyone who is able to compile Gri on the problematic platforms, and who is willing to share their results.

A6.4 Is there a Macintosh version of Gri?

There once was a clicky-pointy Macintosh version of gri, but I got frustrated with modifying the code each time Apple upgraded the OS and stopped maintaining the code. After several years of living (happily) without the Macintosh, I flushed the Mac code down the drain.

However a version for Macintosh unix is available.

A6.5 Is there a DOS/Windows version of Gri?

There is a version available for DOS, available at the normal Gri FTP site, ftp://ftp.phys.ocean.dal.ca/users/kelley/gri, and copy another at the anonymous FTP site ftp://shiho.tokyo-u-fish.ac.jp/pub/msdos/gri with filename of the form gri2025b.zip where 2025 refers to the version name. This binary version was prepared and very kindly shared by Toru Suzuki toru@shiho.tokyo-u-fish.ac.jp. Together with the distribution comes a file called README, which tells how to install and use Gri in an msdos context.

Also, see the Gri manual under the heading "Compilation on PC-style Computers"

As for viewing the output, I recommend obtaining a copy of the Ghostview program (which is a general PostScript display program), in the version called GSview.

A6.6 Is there a linux version of Gri?

For non-RedHat versions of linux, one compiles and installs Gri in the usual way; see the manual for more details.

Users of RedHat linux have it much easier though! A RPM (RedHat Program Manager) version of Gri exists, so that installing it takes just one line of typing, or one mouse-click in the RPM GUI-based installer called `glint'. requires just one line of typing (or

The RPM (RedHat Package Manager) version exists at FTP site ftp://ftp.phys.ocean.dal.ca/users/kelley/gri in a file with a name such as `gri-2.1.17-1.i386.rpm' (RedHat readers will know immediately what all the numbers and dots stand for!) Once you've downloaded this, install Gri by typing

    rpm -i gri-2.1.17-1.i386.rpm
Later on, Gri may be uninstalled ('extracted') by typing
    rpm -e gri

Knowledgeable RedHat users will know that RPM can also give information about Gri; for non-experts, here are a few examples:

    rpm -qa       --  list all installed packages
    rpm -qi gri   --  summarize gri capabilities (if it's installed)
    rpm -ql gri   --  list all files related to gri

A7 Gri bugs

A7.1 What are known bugs in Gri?

Gri is used daily by many users, including the author, so that it suffers few serious bugs. Generally, more recent versions of Gri suffer fewer bugs than earlier versions. This improvement owes much to the trial of daily usage by folks with differing working styles; and all users can thank those who send in bug reports (see Q7.2).

One of the main problems with recent versions of Gri is that line numbers of syntax errors are reported inaccurately, if the error occured inside a new-command.

A list of Gri bugs is maintained in the full manual.

A7.2 How can I report Gri bugs?

The first step is to make sure it is actually a bug. You might try, for example, posting a question to the Gri newsgroup (see Q2.3), and getting advice from other users. Please be clear, so you don't waste others users' time. If you think you've found a bug, let the author know. Here's the advice from the manual (see especially item 4, for directions on emailing bug reports):

Your bug reports help make Gri reliable and useful. Reporting bugs often results in quick changes to gri which will solve your problem. This is especially true if your version is reasonably up-to-date, for then you can simply get the corrected version and replace the version you were using. Here is how to report bugs: