Programming Gri
1: Introduction
2: Simple example
3: Fancy example
4: Running Gri
5: Programming Gri
6: General Issues
7: X-Y Plots
8: Contour Plots
9: Image Plots
10: Examples
11: Handling Data
12: Gri Commands
13: Gri Extras
14: Evolution of Gri
15: Installing Gri
16: Gri Bugs
17: System Tools
18: Acknowledgments
19: License
20: Newsgroup
21: Concept Index
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5.12: Debugging Gri Programs
Here are some hints for debugging Gri programs:
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If no data appear on an xy plot, insert `
show columns statistics '
or `show columns ' after the `read columns ' command. It may be
that you have fixed your axes, and that the axes frame does not include
the data.
-
If you get an error message, rerun your Gri program using the
`
-trace ' command-line option, to see which line is causing the
problem. This often reveals logic errors (e.g. in (`if '
statements). You may also turn tracing on or off at any point in your
Gri program by setting the built-in variable `..trace.. ' to 1 or 0.
Many Gri users have the Gri command aliased to be in trace mode by
default.
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If Gri complains of a syntax error, consult the printed manual, one of
the online manuals, or the online help facility see Online Help.
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Check the version number (printed at startup) to see if a new version of
Gri has been installed. Check the manual for known incompatabilities
see Incompatibilities. You should always have a
`
expecting version .n. ' command in your program, with `.n. '
set to the version of Gri that you are most familiar with. This will
warn of any incompatabilites since the named version.
-
Sprinkle `
show ' commands throughout your program, to see what's
happening. Even when you are sure your program works, it is a good idea
to embed `show ' statements so are they executed if the
`-debug ' flag is set:
if ..debug..
show "X=" .x. "and label is `\label'"
end if
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If your your `
draw ' commands don't draw anything, check to see
whether you've fooled yourself by enforcing an improper scaling; remove
explict scaling (`set x axis ... '), clipping `set clip ', data
selection windows (`set input data window x|y ') and missing values
(`set missing value '). Another trick is to read only a portion of
the data set (`read columns 10 x y ') and then print out all the
values (`show columns ').
If you determine that the bug is in Gri, not in your program, please
report the bug, so that other users will not have the same hassle;
see Bugs.
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