My question is more about math then the actual code.
When use the command
set logscale
on gnuplot 5.0 what is happening ?
It should represents the logarithmic values values of the x and y points.
But it doesn not seems to work properly. For example on my data I have x and y values smaller then 1 so I am expecting to see negative values for these values on the plot, but I see only postivie values.
What I am doing wrong ?
The logarithmic scale still shows the real values around the axes, just their distances are logarithmic. To really see the negative values, you need to really apply the log function:
plot "file.dat" using (log($1)):(log($2)) with lines
without setting the logscale.
A specific example might help to illustrate the effect of logarithmic scaling:
set xrange [0.1:10]
plot x**2
Let's plot this again, but this time on a logarithmic scale. Watch how the scaling of the x and y axes changes:
set logscale
replot
Related
I am trying to plot a function f(x)=exp(-x+10) with the y-values below (and including) y=1. So basically in the range x>=10.
Trying
f(x) = x>=10 ? exp(-x+10) : 1/0
plot f(x)
does not work, because gnuplot starts plotting at y-values greater than 1. Shifting the interval a bit, I can also manage to start at values less than 1, however it seems impossible to hit exactly 1.
I presume this has something to do with precision which causes problems with the steep slope of the exponential.
Still, is there a way to properly plot that function in the specified range?
What about this? I guess you have to set a xrange including an end.
reset session
f(x) = exp(-x+10)
set xrange[10:15]
plot f(x)
When plotting data which are very dense in small ranges of y, the logarithmic scale of gnuplot is the right scale to use.
But what scale to use when the opposite is the case? let's say most y values of different curves are between 90 and 100. In this case I want to use something like a inversed logarithmic scale. I tried a log scale between 0 and 1 but gnuplot wants me to choose a scale greater than 1
How can I achieve this?
You are right, you can use the inverse of the logarithmic function, which is the exponential. But gnuplot only supports logarithmic scales, so you have to do the conversion on your own:
plot "myData" using 1:(exp($2))
You will also have to handle the axis tics on your own. Either you just set them via a list like
set ytics ("0" 1.00, "1" 2.72, "2" 7.39, "3" 20.09, "4" 54.60, "5" 148.41)
or you use the link feature for axes of gnuplot 5. The following code uses the y2axis (right y-axis) to plot the data and calculates the tics on the left y-axis from the right one.
set link y via log(x) inverse exp(x)
plot "myData" using 1:(exp($2)) axes x1y2
Side note: Always remember that a non-linear axis is hard to understand. Logarithmic scales are common, but everything else not. So, be careful when presenting the data
I have 2 datasets which I want to plot on top of each other. The first data set has a yrange of [-10:10], while the second has a range of [-2:2]. If I just plot them on top of each other in the usual linear scale, it is very difficult to see any features of the second data set:
Ideally I would like a nonlinear scale on the y axis to really emphasise what is going on between -2 and 2. I would like to design a y axis which looks like this:
So that most of the middle part of the plot is between -2 and 2. (I just manually added ytics in this figure) Does anyone know how to accomplish this via the "set link" command or something similar?
I am trying to fit a plot in gnuplot using logscale. I have 50000 data points.
At first I fit plot in this way.
f(x) = b + m*x
fit f(x) "xyMSD-all-mal-cel-iso-bcm-thermo2.dat" using 1:2 via m,b
I got slope value. Then I tried to get slope value at different range as below.
fit [30000:50000] f(x) "xyMSD-all-mal-cel-iso-bcm-thermo2.dat" using 1:2 via m,b
The above code works fine. In next attempt I tried,
f(x) = b + m*x
fit f(x) "xyMSD-all-mal-cel-iso-bcm-thermo2.dat" using (log($1)):(log($2)) via m,b
Above works fine too. I get the slope value. Then I tried to choose the xrange like below. This is where I have problem. It does not work.
fit [500:5000] f(x) "xyMSD-all-mal-cel-iso-bcm-thermo2.dat" using (log($1)):(log($2)) via m,b
Is there any way to achieve this?
Appreciate any help
The range has to fit the expression, which in your case are log values. So make sure the log values are within range. For example, if your range for ($1):($2) is [500:5000], then the corresponding range for (log($1)):(log($2)) should be something like [2.69:3.69].
Gnuplot first uses the expression on your data. Limiting the range is the second step, so in this case the logarithm of the required data points have to be in the xrange.
AND don't forget: logscale uses the logarithm based on 10 but log(x) or log($1) means logaritm based on 'e' (approx. 2.7183). To be harmonic with the logscale use function log10(x) (or log(x)/log(10)).
PS: I know that the original question had been answered previously, but I haven't got enough prestige to append my useful comment about the log() function as a comment.
I want to plot some data on x axis range [0:1] and y axis range [0:100], but on the x axis I have most of my data in range [0:0.1] and less data in the rest of the range. I thus wanted to expand the [0:0.1] range. I cannot use a logarithmic scale for the x axis as I have some data which is 0 and I cannot plot it if I use a logarithmic scale. Is there a way for plotting this in Gnuplot?
Ideally I would want to apply a logarithmic scale to the x axis, but start my plot from 0. That would help me to cover all the data and highlight the [0:0.1] range as well. Can it be done?
As you noted, it is impossible to have a logarithmic scale with a 0. I would use two graphs side by side, with separate x axes. You can do this through set multiplot layout 1,2.
I agree with Svante. An other option would be to introduce a second x-axis in the same plot. Then one x-axis would scale from 0:0.1 and the other would scale from 0:1. Depending on your data however this approach could be very confusing but I think especially if your data is primarily located between 0:0.1 this could work.