how to set y-axis as log scale?

I am plotting x-y plot using plot function. I want to set only y-axis as log scale and x-axis as linear? How to do that? I used loglog function but it scales both axis but I want only Y.

Answer 1

[Walter Roberson]

The best way to create that type of axes is to use the semilogy function. Alternatively, you can set the ‘YScale’ property on the axes:

set(gca, 'YScale', 'log')

[Nick Durkee]

Note that this works for 3D plots as well. Not sure if there's an equivalence of semilogx for 3d.

[Walter Roberson]

set(gca, 'XScale', 'log')

[Mahender Aroori]

thank you

[M S Rashed]

Is there any way to convert from log-scale back to linera scale?

[Yang Yang]

set(gca, 'XScale', 'linear')

[In-chan Kim]

Is there a way to make set(gca, 'YScale', 'log') show negative values as well?

[Walter Roberson]

The log of negative real values is equal to the log of the positive value, plus (pi*1i) -- that is the result is complex. When you set YScale to log, then internally it would take the log of the negative values you have, and would found that the log is complex.

If, hypothetically, it were able to display with complex coordinates, where would you want the values displayed? For example do you want the complex portion of the coordinate to be treated as time, and the display should automatically cycle through a time period (perhaps every 2*pi seconds) with the negative values being displayed for one frame on each occasion that the complex value projected down to real?

If you want negative values to be displayed where the corresponding positive value would be displayed, then plot with abs(y) instead of y.

Remember, when you use log, there is an infinite distance in log scale between y = 1 and y = 0, since it has to pass through y = exp(-1), y = exp(-2), y = exp(-3), and so on, each of which needs to be allocated the same screen distance as between y = exp(0) and y = exp(1) . To get to negative y, you would have to go "further than infinity" down the bottom of the plot.

[Brad Norton]

what is gca?

[Walter Roberson]

https://www.mathworks.com/help/matlab/ref/gca.html

ax = gca returns the current axes or chart for the current figure, which is typically the last one created or clicked with the mouse.

[samane pahlevani]

Hi . I want to plot y-axis scale as log10. how can I do that? I tried your answer but log in matlab is based on 'e' not 10!

[Walter Roberson]

@samane pahlevani

How can you tell whether the y-axes scale is log10 or natural log?

The labeling is always done based on log10, no matter whether the underlying graph is log10 or log e.

Suppose the calculation were done log B for some base B. Then log[B](x) = log[e](x) * log[e](B) which is a constant multiple relative to log[e] . The constant multiple would alter how much height the graph would need, but as a magnification, not as a change to the shape of the graph. And the size available to plot into is fixed, so MATLAB is just going to rescale anyhow...

[samane pahlevani]

I'm really grateful for your help. I completely figured out your answer. Just about the formula which you wrote, I suppose that the accurate form would be: log[B](x) = log[e](x) / log[e](B)

[Walter Roberson]

You are correct, it should have been division not multiplication.

[Weirong Sun]

good answer! It's very helpful!!!

Answer 2

[Elkin Javier Cepeda Ramirez]

thank you , you help me too much

[Samuel Pulpan]

Thanks

Answer 3

[Hazem Mubarak]

Thanks ;)

Answer 4

[Rohit Sinha]

The easiest way to do this is simply use the following command instead of plot

semilogy(x,y);

This will plot x axis on a linear scale and y axis on a log scale. Similarly, if you want to plot x axis on log scale and y axis on a linear scale, you can use

semilogx(x,y) ;

[Walter Roberson]

semilogy() is the first thing I mentioned in my answer in 2016.