I'm trying to plot this function with gnuplot
but when I try to do it a find this Warning: empty y range [1:1], adjusting to [0.99:1.01]. I think that it should be a precision problem. I can plot it perfectly in another programs, but I would like to know why I can not plot it with gnuplot and how to fix it
Edit:
The command that I'm using is
f(x)=(1-(sinh(1/x))**(-4))**(1/8)
plot [0.01:1.131] f(x)
Two things:
That equation as written does not match the one you showed. Is the exponent supposed to be 4 or -4?
Gnuplot uses integer arithmetic, so (1/8) evaluates to 0. Use either (1./8.) or (.125)
Possible correction (depending on what is the correct exponent):
f(x) = (1. - (sinh(1/x)**(-4)))**(1./8.)
set xrange [0.01 : 1.131]
plot f(x)
Related
is there a way to avoid the drawing of the near asymptote line in the function 1/(2-x), for example, without usage of conditional plotting? The idea is to draw iterated functions based in this one and, since asymptote changes, using conditional plotting isn't a good solution.
You can plot with points at a very high sampling rate:
set yrange [-10:10]
set samples 100000
plot 1/(2-x) with points
If the singularity occurs at different values of x you can use conditional plotting on y:
f(x)=1/(2-x)
set samples 1000
plot (abs(f(x)) < 10 ? f(x) : 1/0) with lines
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 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 am trying to plot multiple parametric curves in gnuplot 4.6.
In an earlier version (4.4?), the commands
set para
plot [-pi:pi] for [a=1:10] a*cos(t),a*sin(t)
would result in ten circles centered at the origin with radius 1, 2, ..., 10. In 4.6, the result is one circle of radius 1.
In 4.6, the commands
unset para
plot [-pi:pi] for [a=1:10] a*sin(x)
yield ten beautiful sine curves.
So, it appears that the "for" command now has a problem with parametric curve plotting, I guess.
Does anyone know of a workaround? The circle object is not useful for me: I am interested in general curves. Thanks!
The syntax ambiguity between parametric mode and iteration is a documented bug/limitation in current gnuplot versions. In the development version (4.7) a separate parametric mode is not necessary, as the required sampling variable can be explicitly described in a generic plot command:
plot for [a=1:10] [t=-10:10] '+' using (a*sin(t)):(a*cos(t))
Unfortunately that fully general syntax is not available in version 4.6. The closest I can think of is a simpler variant:
unset parametric
plot for [a=1:10] '+' using (a*sin($1)):(a*cos($1))
This works for your example case, but may not suffice for your actual use case because it conflates the sampling range on the parametric variable with the implicit plotting range on x.
I have to plot an histogram in logarithmic scale on both axis using gnuplot. I need bins to be equally spaced in log10. Using a logarithmic scale on the y axis isn't a problem. The main problem is creating the bin on the x axis. For example, using 10 bins in log10, first bins will be [1],[2],[3]....[10 - 19][20 - 29].....[100 190] and so on. I've searched on the net but I couldn't find any practical solution. If realizing it in gnuplot is too much complicated could you suggest some other software/language to do it?
As someone asked I will explain more specifically what I need to do. I have a (huge) list like this:
1 14000000
2 7000000
3 6500000
.
.
.
.
6600 1
8900 1
15000 1
19000 1
It shows, for example, that 14 milions of ip addresses have sent 1 packet, 7 milions 2 packets.... 1 ip address have sent 6600 packets, ... , 1 ip address have sent 19000 packets. As you can see the values on both axes are pretty high so I cannot plot it without a logarithmic scale.
The first things I tried because I needed to do it fast was plotting this list as it is with gnuplot setting logscale on both axes using boxes. The result is understandable but not too appropriate. In fact, the boxes became more and more thin going right on the x axis because, obviously, there are more points in 10-100 than in 1-10! So it became a real mess after the second decade.
I tried plotting a histogram with both axis being logarithmically scaled and gnuplot through the error
Log scale on X is incompatible with histogram plots.
So it appears that gnuplot does not support a log scale on the x axis with histograms.
Plotting in log-log scale in GnuPlot is perfectly doable contrary to the other post in this thread.
One can set the log-log scale in GnuPlot with the command set logscale.
Then, the assumption is that we have a file with positive (strictly non-zero) values both in the x-axis, as well as the y-axis. For example, the following file is a valid file:
1 0.5
2 0.2
3 0.15
4 0.05
After setting the log-log scale one can plot the file with the command:
plot "file.txt" w p where of course file.txt is the name of the file. This command will generate the output with points.
Note also that plotting boxes is tricky and is probably not recommended. One first has to restrict the x-range with a command of the form set xrange [1:4] and only then plot with boxes. Otherwise, when the x-range is undefined an error is returned. I am assuming that in this case plot requires (for appropriate x-values) some boxes to have size log(0), which of course is undefined and hence the error is returned.
Hope it is clear and it will also help others.
Have you tried Matplotlib with Python? Matplotlib is a really nice plotting library and when used with Python's simple syntax, you can plot things quite easily:
import matplotlib.pyplot as plot
figure = plot.figure()
axis = figure.add_subplot(1 ,1, 1)
axis.set_yscale('log')
# Rest of plotting code