I'm an happy user of the with vectors options in Gnuplot. However, in most case, the vectors need to be rescaled to make a nice figure.
Currently, I am doing this by
plot "data" using 1:2:($3*scale):($4*scale) with vectors
Ideally, I would just like to skip using and writing the scale for vector-length manually once, such that I could use
plot "data" with vectors scale 0.1
Maybe there is an auto-scaling option that I am unaware of?
There's no shortcut for that as far as I know. The best you'll probably do is to use a macro:
set macros
with_vectors = "using 1:2:($3*scale):($4*scale) w vectors"
scale = 0.1
plot "data" #with_vectors
scale = 0.2
plot "data" #with_vectors
Related
I am new to Gnuplot and unfortunately have to start with a (for me) nontrivial problem. I have X-Y-Z-Temperature data. So I have for every spatial coordinate a temperature value.
This comes somewhat closest
http://pgfplots.net/tikz/examples/contour-and-surface/
However, I would like to create a heat map (not contour) on the XY XZ and YZ plane to visualise the 4D data better (in the link it is just 3D).
So on each plane just a heat map using the same color code so that the temperatures can be compared.
Many thanks!
Toby
You can make '4d' plot with palette, e.g:
splot '3d.dat' u 1:2:3:4 palette pt 9
So you mean e.g. plotting a triedron T(x,y,z=0), T(x=0,y,z) and T(x,y=0,z) ? This should be possible with multiplot and rotating the view between each plot. This will be a fair amount of hacking, so the first question would be why you don't use other visualization software like paraview or mayavi ? These are more suited for this type of data, unless you need the flexibility of gnuplot either in terms of scripting, or in terms of plotting analytical functions on the same graph.
gnuplot will plot a data file with vectors.
I would like to set something like isosamples=40 and
have gradient vectors plotted for a 2D function.
I know I could write a python program to generate
the data file for the vectors but
I would prefer to do the entire operation within gnuplot.
Any advice?
Would this be a worthy improvement to gnuplot if not yet implemented?
You can use the vectors style and do the computations in gnuplot using the special filename ++.
Suppose that I wish to graph a direction field for the differential equation y'=y*sin(x). I could do this with the following:
set xrange[-2:2]
set yrange[-2:2]
set samples 30
set isosamples 30
unset key
f(x,y) = y*sin(x)
lf(x,y) = sqrt(1+f(x,y)**2)
lyf(x,y) = f(x,y)/lf(x,y)
plot '++' u 1:2:(0.1/lf($1,$2)):(0.1*lyf($1,$2)) with vectors
All of my calculations are done in gnuplot. I compute the direction of the vectors, and scale them to have a length of 0.1, all in the plot command.
I use the special filename '++' which generates a set of points equally spaced over the x and y plot ranges.
See 'help special-filenames' for more details on that.
i try to fit this plot as you cans see the fit is not so good for the data.
My code is:
clear
reset
set terminal pngcairo size 1000,600 enhanced font 'Verdana,10'
set output 'LocalEnergyStepZoom.png'
set ylabel '{/Symbol D}H/H_0'
set xlabel 'n_{step}'
set format y '%.2e'
set xrange [*:*]
set yrange [1e-16:*]
f(x) = a*x**b
fit f(x) "revErrEnergyGfortCaotic.txt" via a,b
set logscale
plot 'revErrEnergyGfortCaotic.txt' w p,\
'revErrEnergyGfortRegular.txt' w p,\
f(x) w l lc rgb "black" lw 3
exit
So the question is how mistake i compute here? because i suppose that in a log-log plane a fit of the form i put in the code should rappresent very well the data.
Thanks a lot
Finally i can be able to solve the problem using the suggestion in the answer of Christop and modify it just a bit.
I found the approximate slop of the function (something near to -4) then taking this parameter fix i just fit the curve with only a, found it i fix it and modify only b. After that using the output as starting solution for the fit i found the best fit.
You must find appropriate starting values to get a correct fit, because that kind of fitting doesn't have one global solution.
If you don't define a and b, both are set to 1 which might be too far away. Try using
a = 100
b = -3
for a better start. Maybe you need to tweak those value a bit more, I couldn't because I don't have the data file.
Also, you might want to restrict the region of the fitting to the part above 10:
fit [10:] f(x) "revErrEnergyGfortCaotic.txt" via a,b
Of course only, if it is appropriate.
This is a common issue in data analysis, and I'm not certain if there's a nice Gnuplot way to solve it.
The issue is that the penalty functions in standard fitting routines are typically the sum of squares of errors, and try as you might, if your data have a lot of dynamic range, the errors for the smallest y-values come out to essentially zero from the point of view of the algorithm.
I recently taught a course to students where they needed to fit such data. Lots of them beat their (matlab) fitting routines into submission by choosing very stringent convergence criteria, but even this did not help too much.
What you really need to do, if you want to fit this power-law tail well, is to convert the data into log-log form and run a linear regression on that log-log representation.
The main problem here is that the residual errors of the function values of the higher x are very small compared to the residuals at lower x values. After all, you almost span 20 orders of magnitude on the y axis.
Just weight the y values with 1/y**2, or even better: if you have the standard deviations of your data points weight the values with 1/std**2. Then the fit should converge much much better.
In gnuplot weighting is done using a third data column:
fit f(x) 'data' using 1:2:(1/$2**2") via ...
Or you can use Raman Shah's advice and linearize the y axis and do a linear regression.
you need to use weights for your fit (currently low values are not considered as important) and have a better starting guess (via "pars_file.pars")
I have been wondering about this for a while, and it might already be implemented in gnuplot but I haven't been able to find info online.
When you have a data file, it is possible to exchange the axes and assign the "dummy variable", say x, (in gnuplot's help terminology) to the vertical axis:
plot "data" u 1:2 # x goes to horizontal axis, standard
plot "data" u 2:1 # x goes to vertical axis, exchanged axes
However, when you have a function, you need to resort to a parametric function to do this. Imagine you want to plot x = y² (as opposite to y = x²), then (as far as I know) you need to do:
set parametric
plot t**2,t
which works nicely in this case. I think however that a more flexible approach would be desirable, something like
plot x**2 axes y1x1 # this doesn't work!
Is something like the above implemented, or is there an easy way to use y as dummy variable without the need to set parametric?
So here is another ugly, but gnuplot-only variant: Use the special filename '+' to generate a dynamic data set for plotting:
plot '+' using ($1**2):1
The development version contains a new feature, which allows you to use dummy variables instead of column numbers for plotting with '+':
plot sample [y=-10:10] '+' using (y**2):(y)
I guess that's what come closest to your request.
From what I have seen, parametric plots are pretty common in order to achieve your needs.
If you really hate parametric plots and you have no fear for a VERY ugly solutions, I can give you my method...
My trick is to use a data file filled with a sequence of numbers. To fit your example, let's make a file sq with a sequence of reals from -10 to 10 :
seq -10 .5 10 > sq
And then you can do the magic you want using gnuplot :
plot 'sq' u ($1**2):($1)
And if you uses linux you can also put the command directly in the command line :
plot '< seq -10 .5 10' u ($1**2):($1)
I want to add that I'm not proud of this solution and I'd love the "axis y1x1" functionality too.
As far as I know there is no way to simply invert or exchange the axes in gnuplot when plotting a function.
The reason comes from the way functions are plotted in the normal plotting mode. There is a set of points at even intervals along the x axis which are sampled (frequency set by set samples) and the function value computed. This only allows for well-behaved functions; one y-value per x-value.
I have a problem with gnuplot. I've searched and I don't find the correct solution. I'm plotting some data arranged in three columns with the command splot, and the steps in x and y are different. The plot I get with:
set view map
splot 'data.dat' using 1:2:3 with points palette
is:
and I would like the white space to be filled, making each tile size adapt, avoiding interpolation.
Some ideas are given here Reduce distance between points in splot.
I've tryed http://gnuplot.sourceforge.net/demo/heatmaps.html too, but with image doesn't seem to work :(
I should avoid pointsize as my grid changes from time to time.
You can try
set pm3d map interpolate 1,1 corners2color c1
splot 'data.dat' using 1:($2-5e-5):3
This uses no interpolation, and the color of each polygon depends on the value of corner 'c1'. You may need to test if this is the correct one, or if you need 'c2', 'c3', or 'c4'.
Another solution to my problem, better than this one for some terminals at least, is given in the answers to my other question about maps appearance in pdfcairo terminal, where the solution comes when using plot with image insted of this splot. I tried to use that before, as I mention here, but maybe it also needed this specific data format.