What the 'set logscale' does in gnuplot?

Question

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 ?

Check [Logarithmic scale](https://en.wikipedia.org/wiki/Logarithmic_scale) at Wikipedia, especially the **log-log** graph. — choroba, Mar 29 '18 at 15:38
I had already checked on wikipedia before to ask but I don't understand why I don't see negative value for values smaller than one.. — Andrea Angeletti, Mar 29 '18 at 17:09
Andrea, put `set format xy "10^{%L}"` to fix the axes labels — Gavin Portwood, Mar 30 '18 at 14:56

score 2 · Answer 1 · answered Mar 29 '18 at 21:45

2

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

answered Mar 29 '18 at 21:45

user8153

4,049
1
9
18

score 1 · Answer 2 · answered Mar 29 '18 at 17:21

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.

What the 'set logscale' does in gnuplot?

2 Answers2