how to set y-axis as log scale?

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Rohit Bhoi 2016-4-15

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评论： Adam Danz 2024-7-12，15:08

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

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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.

Mr Thadi 2024-7-4，5:31

data.mat

Thank you Mr walter,

i have attached one image,

in that my data file having values from 100 to 14000.

if i plot histogram without x axis set properties it showing like figure 'A', in that bins starts from 0-300,300-600...etc like that.

but if i use set (gca,'xscale','log') command to the x scale it showing initial bin from 300-600,600-900....etc.you can see in figure 'B'

my question is what about values in between 0-300 from figure 'B' , why these are not appearing how to solve it,if i want to get xscale in log values histogram initial bin from 0-300,300-600...etc are needed to change properties in that to command?can you please explain me

i can provide my data file also to you

Adam Danz 2024-7-12，15:08

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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

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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) ;