Question

I am trying to plot (with Gnuplot) some basic 3d data from one file which is pretty much like that:

N     M    t1      t2       t3       t4
1000 1000 0.05268 0.04711 0.003947 0.003348
1000 2000 0.05743 0.04214 0.007577 0.006486
1000 3000 0.08465 0.04193 0.011329 0.009654


2000 1000 0.10726 0.08845 0.013593 0.012397
2000 2000 0.21065 0.10817 0.026525 0.024390
2000 3000 0.31528 0.16960 0.039772 0.036405


3000 1000 0.25415 0.14845 0.031082 0.026364
3000 2000 0.47345 0.25227 0.060887 0.051840
3000 3000 0.70612 0.36866 0.091311 0.077432

The idea is to plot it in some way I could see t1,t2,t3 and t4 for each N and M. It may be a lot of data to plot in only one graph, I know that. First of all, I have started with t1 plotting this way:

splot 'aux' u 1:2:3 w lp

and I get something like that

I would like to smooth a bit those lines and give them a different color. Is there any way to do something for it? Also any ideas to improve it in any other way would be very nice.

Answer 1

You’re right, that is a lot of data. Changing the color of a particular dataset is pretty easy:

splot "dataset" using 1:2:3 w lines linecolor rgb "green"

Note that you can easily overlay multiple plots as follows:

splot "dataset" using 1:2:3 w lines lc rgb "green",\
      ""        using 1:2:4 w lines lc rgb "red"

A backslash at the end of a line is the gnuplot line-continuation character. Note that it must be the last character on the line. I’ve also used the pseudo-file "" which is just shorthand for the last file that gnuplot read. Finally, in this second version I used lc instead of linecolor. The gnuplot parser provides a lot of shorthand, although I suspect you already know this since you plotted w lp. (Also, please don’t actually choose red and green for your plots. I think one of the biggest flaws in gnuplot is the default first 2 colors are red and green — 1 in 20 people is red-green colorblind)

Smoothing is another story (unfortunately). plot does support a smooth option

plot "dataset" using 1:2 smooth beizer with lines  #see help smooth for a list of options

Unfortunately, it appears that this option doesn’t work for splot. At this point, I would write a small utility script to smooth the data in your favorite language using your favorite smoothing algorithm (plot "<utility.script mydata" u 1:2:3 ...). There are other (gnuplot-only) options, but they’d be ugly. What version of gnuplot do you have by the way? The gnuplot version is important to decide the best way to do the smoothing all in gnuplot if you decide that’s still necessary.