Re: 2d vector fields

[Ethan A M. <merritt@u.washington.edu>]

On Sunday 15 April 2007 00:44, Pawel Cesar Sanjuan Szklarz wrote:
> Hi.
> the plot
> splot '+' 1:2:(sin($1)*$2*$2):(cos($2)*$1*$1) with vectors
> is not working. I not found any splot with vectors example in the demo files:
> bash: grep splot * | grep vectors

I did not have the command quite right.  I was forgetting that for splot you
need to give a z coordinate for each endpoint, even if they are all the same.

This works:
    set samples 10
    set isosamples
    set xrange [0:1]
    set yrange [0:1]
    set view map
    splot '+' using 1:2:0:(sin($1)/20.):(cos($2)/20.):0 with vectors
 
> But what I need is a 2d plot with vectors, the same as

Yes, if you are reading the coordinates from a file then you can do this
with "plot".   But in order to auto-generate a 2D grid, you need to use
"splot".  The normal use for splot is to generate 3D plots, by associating
a Z value with each [x,y] sample.  However, my example above re-uses the
x and y coordinates to calculate each end of a vector in the plane Z=0.

I have attached the output of my example as an *.eps file. 
As I said, this is a very new feature, and you may be able to suggest
enhancements to make it better. 

	Ethan

 
> gnuplot>plot 'mydataField.dat' using 1:2:3:4 with vectors
> 
> where in the file 'mydataField.dat' I have
> x y sin(x)*y^2 cos(y)x^2
> calculated for all points.
> 
> I would like to get the same using something like special functions:
> gnuplot>plot '+' using 1:2:(sin($1)*$2*$2):(cos($2)*$1*$1) with vectors
> 
> Pawel Szklarz.
> 
> 2007/4/14, Ethan A Merritt <merritt@u.washington.edu>:
> > On Saturday 14 April 2007 10:29, Pawel Cesar Sanjuan Szklarz wrote:
> > > Hi
> > >
> > > I am interested in add a feature do gnuplot: 2d vector fields from
> > > R^2->R^2 functions
> > >
> > > example:
> > > gnuplot>plot (sin(x)*y^2,cos(y)x^2) with 2dVectorField
> >
> > Please have a look at the very recent feature added to the cvs version:
> >
> > gnuplot> help special-filenames
> >  There are three filenames that have a special meaning:  '', '-', and '+'.
> >  The special filename '+' is a mechanism to allow the full range of
> >  `using` specifiers and plot styles with in-line functions.  Normally a
> >  function plot can only have a single y (or z) value associated with each
> >  sampled point.  The pseudo-file '+' treats the sampled points as columns
> >  1 (plot) or 1 and 2 (splot), and allows additional column values to be
> >  specified via a `using` specification, just as for a true input file.
> >  Example:
> >        plot '+' using ($1):(sin($1)):(sin($1)**2) with filledcurves
> >
> >
> > You may be able to use this new mechanism to do your plotting.
> > Or maybe not.  I'm not sure I understand what is the intended output
> > from your example.  Is it a set of vectors, with each vector connecting
> > (x,y) to (sin(x)*y^2, cos(y)*x^2) ?   That would be something like
> >         splot '+' 1:2:(sin($1)*$2*$2):(cos($2)*$1*$1) with vectors
> > You may have to change "set isosamples" first.
> >
> > Of course Octave doesn't yet know about this option, but I'm sure
> > that can be fixed.
> >
> >
> >
> > >
> > > I know that it is possible to create a datafile with the information
> > > about the vector field, but it can be nice to make zoom and don't
> > > worry about the data density in the datafile.
> > >
> > > I would like to add another feature: I would like to use octave (for
> > > example) to calculate the value of some function.
> > > My proposition is not to run octave many times, but to create a
> > > children process and send/recibe values by PIPES, example:
> > >
> > > gnuplot>open calculator 'myCulculatorProgram'
> > >   now gnuplot forks and create a children process
> > > "system('myCulculatorProgram')" and is ready to use that program to
> > > calculate something (open 2 pipes gnuplot<-->Mycalculator)
> > > gnuplot>plot calculator('myExternalFunctionName',x,y)
> > >   To calculate the value of
> > >    calculator('myExternalFunctionName',x,y)
> > >  gnuplot send data by the pipe to the children process and white for
> > > the results in another pipe.
> > >
> > > This feature can by really great, octave is what I need, but with this
> > > mechanism it is possible even to send SOAP request to some special
> > > mega-calculation-server or what ever.
> > >
> > > I have ready some code for this feature, but i would like to know:
> > > --can be this useful?
> > > -- it is possible to make something equivalent with gnuplot in some other way
> > > And if this is a new feature, then:
> > > -- what format to use for this features (represent R2->R2 functions,
> > > and the external calculator)
> > > -- how to submit code to CVS
> > >
> > > Thanks
> > >
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> >
> > --
> > Ethan A Merritt
> > Biomolecular Structure Center
> > University of Washington, Seattle 98195-7742
> >
> 
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-- 
Ethan A Merritt
Biomolecular Structure Center
University of Washington, Seattle 98195-7742