how to set y-axis as log scale?

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Rohit Bhoi on 15 Apr 2016

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Commented: Nicholas Santiagoon 4 Nov 2022

Accepted Answer: Walter Roberson

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.

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Walter Roberson on 15 Apr 2016

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Edited:MathWorks Support Team on 28 Nov 2018

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')

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Walter Roberson on 30 Apr 2020

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.

Weirong Sun on 9 May 2022

good answer! It's very helpful!!!

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Rohit Sinha on 27 Apr 2022

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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) ;