Graphics with Gnuplot from C and Python language

Posted by ionut
September 30, 2008

If you are doing a lot of calculations/simulations, like me, using C or/and Python language, you also need to visualize your simulated data. One way to do it is just to generate/write a “data” file and plot it with your plotting preferred package after the simulation is finished. But maybe, sometimes, you want to see the graph in real time, so, here I would like to show a small C and Python program which calls Gnuplot and save the plot in png format.

C Example:

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#include<stdio.h>
/*
	Author: Ioan Vancea (www.vioan.ro)
	*****************************/
int main()
{
	FILE *pipe = popen("gnuplot -persist","w");
	fprintf(pipe, "set samples 40\n");
	fprintf(pipe, "set isosamples 40\n");
	fprintf(pipe, "set hidden3d\n");
	fprintf(pipe, "set xrange [-8.000:8.000]\n");
	fprintf(pipe, "set yrange [-8.000:8.000]\n");
	fprintf(pipe, "set zrange [-2.000:2.000]\n");
	fprintf(pipe, "set terminal png\n");
	fprintf(pipe, "set output 'graph.png'\n");
	fprintf(pipe, "set title 'We are plotting from C'\n");
	fprintf(pipe, "set xlabel 'Label X'\n");
	fprintf(pipe, "set ylabel 'Label Y'\n");
	/* fprintf(pipe, "plot 'datafile.dat' using 1:2\n");*/
	fprintf(pipe, "splot cos(x)+cos(y)\n");
 
  close(pipe);
  return 0;
}

The output:

Python Example (I use Gnuplot.py):

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#!/usr/bin/env python
 
'''
	Author: Ioan Vancea (www.vioan.ro)
'''
 
import math
import Gnuplot
gp = Gnuplot.Gnuplot(persist=1)
x = range(1000)
y = [math.sin(a) + math.cos(a) + math.tan(a) for a in x]
data = Gnuplot.Data(x, y, title='Plotting from Python')
gp('set data style lines')
gp('set xlabel "Label x"')
gp('set ylabel "Label y"')
gp.plot(data);
gp.hardcopy(filename="pyplot.png",terminal="png")

The output:

Gnuplot, Python, SciComputing

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Comments
Pingback by Calling Gnuplot from Perl | Ionut's WebSpace on September 30, 2008 @ 11:18 pm

[...] my previous post I discussed how to call Gnuplot from C and Python language. If you are using Perl, then, here is [...]

Comment by Nicolas on October 2, 2008 @ 11:27 am

You may want to check out this page, it has some information about calling gnuplot from C, C++, Python and others:
http://ndevilla.free.fr/gnuplot/
Hope it helps

Comment by ionut on October 2, 2008 @ 9:54 pm

Thanks Nicolas, nice, I didn’t know about “gnuplot_i”.

Comment by Craig Finch on January 7, 2009 @ 11:59 pm

I like the Pylab/Matplotlib package:
http://matplotlib.sourceforge.net/
If you are familiar with plotting in Matlab, it will be easy to pick up. I have found it to be very good for publication-quality 2D graphics (it doesn’t do 3D).

Comment by Dan on March 19, 2009 @ 11:02 pm

Hi,

I would be interested in bidirectional piping of gnuplot. I want to use gnuplot for both plotting and fitting in my code, and I want to read gnuplot’s output. Is it possible to do?
Thanks,
Dan

Comment by ionut on March 26, 2009 @ 10:42 pm

I didn’t try that, but I think you can also use some intermediate/temporary files for that.

Comment by shreyas on September 3, 2009 @ 5:06 am

Hey i wanted to know if there is a way of plotting graphs from my c++ program without saving the data on to a file.. I am generating random numbers and calculating their averages… I need the averages to be plotted on the graph but i dont want to save the averages to a file.

Thanks

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