how to set y-axis as log scale?

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Rohit Bhoi 2016-4-15

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评论： Mr Thadi 2024-9-29

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 2023-9-22

55
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编辑：MathWorks Support Team 2023-9-22

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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')

***Update from Mathworks Support Team - September 2023***

As of R2023b, you can also use the 'yscale ' function.

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.

Adam Danz 2024-7-12

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This issue arises because the first bin edge is at x=0 and log(0)=-inf which cannot be represented graphically.

Assuming there are no data less than or equal to 0 and no bin edges less than 0, you could set the first bin edge according to the smallest value in the data.

x = rand(1,1000)*10000;

minPositiveValue = min(x(x>0),[],'all');

minbin = 10^floor(log10(minPositiveValue));

ax = axes();

h = histogram(ax, x);

ax.XScale = 'log';

if h.BinEdges(1) == 0

h.BinEdges(1) = minbin;

end

Mr Thadi 2024-9-29

Thank you Mr Adam Danz

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Toshia M 2023-9-20

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Starting in R2023b, you can change the scale of any axis after you create the plot by calling the xscale, yscale, or zscale function.

For example, create a plot of two vectors x and y. Then set the scale of the y-axis to logarithmic.

x = 1:100;

y = x.^2;

plot(x,y)

grid on

yscale log

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Rohit Sinha 2022-4-27

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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) ;