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Re: gnuplot image code

From: John W. Eaton
Subject: Re: gnuplot image code
Date: Wed, 25 Oct 2006 13:30:45 -0400

On 25-Oct-2006, Quentin Spencer wrote:

| Good point. I assumed it was something that would not likely be changed 
| during an octave session, and that calling gnuplot just to get the 
| version would be slow and undesirable to repeat. However, I suppose 
| plotting is not ususally done in speed critical sections of code, so 
| maybe this isn't necessary.

Or, maybe we should arrange for the code that actually invokes the
gnuplot process to run "gnuplot --version" to extract the version
number, then restart gnuplot to actually do the plotting.  The version
number could then be stored for each figure, so doing

  gnuplot_binary ("gnuplot-4.2");
  figure (1)
  image (...)
  gnuplot_binary ("gnuplot-4.0");
  figure (2)
  image (...)
  figure (1)  # switch back to figure 1, which already has gnuplot running
  image (...)

would work.

Even on the slowest system I could find (230MHz Pentium MMX), running
"gnuplot --version" only takes .3s the first time, and about .025s
after that, so the overhead should not be too big.  How long does it
take on a typical system using Cygwin, where process creation is known
to be slow?

The __gnuplot_version__ function could return the version for the
current figure, or -1 if there is no figure currently open.

| By native format, you mean the text format that is normally used for 
| communicating with gnuplot? I suppose that could be done, but eventually 
| when gnuplot 4.2 is widely used, I think it would be good for octave to 
| use the binary format because it will be noticeably faster for large 
| data sets.

No, I meant the native binary floating point format, whatever that
happens to be.  Is it necessary to force Octave to write the data in
ieee-le format?  Isn't the default for gnuplot whatever the native
format is, or is it necessary to tell it the format?


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