From owner-help-octave at bevo dot che dot wisc dot edu  Tue Nov 19 18:46:39 1996
Subject: Variables in gnuplot commands
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Ronald Kumon <kumon at physics dot utexas dot edu>
Cc: Octave Help Listserv <help-octave at bevo dot che dot wisc dot edu>
Date: Tue, 19 Nov 1996 18:46:11 -0600

On 17-Nov-1996, Ronald Kumon <kumon at physics dot utexas dot edu> wrote:

: Does anyone know why you cannot use variables in gnuplot "set" commands 
: from within Octave?

Yes.

: For example, in gnuplot you can execute the commands:
: 
: gnuplot> xsize=0.5
: gnuplot> ysize=0.5
: gnuplot> set size xsize,ysize
: gnuplot> show size
: 
:          size is scaled by 0.5,0.5
:          no attempt to control aspect ratio
: 
: However, the corresponding commands in octave give:
: 
: octave> xsize=0.5
: octave> ysize=0.5
: octave> set size xsize,ysize
: octave>          line 0: undefined variable: xsize

This happens because Octave only parses the set command by noting that
it is a set command and then passing all the remaining text (up until
the next newline or semicolon) directly to gnuplot.  It never notices
that there might be variables that should be expanded.

: Interestingly enough, variable substitution does occur automatically
: in the gplot command since
: 
: octave> ltnum=3
: octave> gplot "data" using 1:3 with lines ltnum 
: 
: will successfully plot columns 1 and 3 of "data" with a line of linetype 3.

This works because Octave does parse the complete gplot command, and
performs the appropriate variable substitutions.  Doing the same for
the set command would be a lot of work because gnuplot's set command
has a lot of different options.  I'm not sure that it is worth the
effort.

Thanks,

jwe