From help-octave-request at bevo dot che dot wisc dot edu Wed Nov 26 12:34:28 2003
Subject: strange behavior from gnuplot
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Mikel Maron <mikel_maron at yahoo dot com>
Cc: help-octave at bevo dot che dot wisc dot edu
Date: Wed, 26 Nov 2003 12:33:53 -0600

On 26-Nov-2003, Mikel Maron <mikel_maron at yahoo dot com> wrote:

| I have just begun using octave (on cygwin), having worked with matlab
| at my university.
| 
| As a first try, I ran my small matlab file, which plots a set of
| differential equations (the Lokta-Volterra predator-prey model).
| 
| After plotting several dozen points, with "hold on", gnuplot slows down
| significantly, and after several hundred points, freezes completely. My
| fuzzy diagnosis: gnuplot can only hold so many plots, even if there are
| simply a single point.
| 
| Perhaps there is something naive in my code/plot. Perhaps something
| else. Suggestions and help much appreciated. Code is pasted in below.

In Octave, "hold on" followed by a series of plot commands is
implemented by doing something that is essentially equivalent to a
series of commands like this in gnuplot:

  plot x1
  replot x2
  replot x3
  ...

which gnuplot handles by creating ever longer plot commands, then
replotting everything.  Also, since Octave's interface with gnuplot
uses temporary files to store the data, you are generating one data
file for every plot command.

It would probably be much better if you cached all the data you want
to plot, then issued a new single plot command for each update with
hold off.

jwe



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