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Re: gnuplot dependency in octave

On  8-Dec-2005, Igor Pechtchanski wrote:

| What about <> (which
| fails gracefully if gnuplot isn't installed)?  Or does octave-forge
| already "do the right thing" (tm) with respect to a missing gnuplot (i.e.,
| print out a meaningful error message, such as "plotting disabled since
| gnuplot is not installed -- please install it to plot")?

Here is what Octave does if it tries to run a nonexistent gnuplot:

  octave:1> gnuplot_binary = "foobar"
  gnuplot_binary = foobar
  octave:2> sombrero (41)
  octave:3> sh: foobar: command not found

  warning: connection to external plotter (pid = 25466) lost --
  warning: please try your plot command(s) again
  warning: broken pipe -- some output may be lost

So the user gets some idea that there is a problem, but I would bet
that this will confuse a lot of people.

My preference would be for it to work out of the box, but that is not
really the case yet, even if you have the gnuplot package installed.
The problem is that the Cygwin version of gnuplot requires X to put a
pretty plot on the screen but Octave does not require X to start.  So
if you run Octave in a Cygwin terminal (no X) then try a plot command,
Octave will think that the plot command succeeded, but nothing will
appear on the screen.  Maybe gnuplot should be giving an error when
the terminal is set to X11 but the X server is not available, but it
does not.

The gnuplot sources already have a way to open a native Windows window
for plotting, but that code is not used for the Cygwin version of
gnuplot (which uses X instead of the native Windows terminal driver).
It would be really sweet if the Cygwin gnuplot could be made to use
the native Windows terminal driver.


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