How to get the ticks for each value of the logarithmic scale?

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Tahariet Sharon 2018-2-26

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https://ww2.mathworks.cn/matlabcentral/answers/384950-how-to-get-the-ticks-for-each-value-of-the-logarithmic-scale

评论： Star Strider 2018-2-26

Hi,

I'm learning to read logarithmic graphs and haven't found anywhere what the ticks between 10^0 and 10^1 for instance are (they are not 10^.1, 10^.2, etc because the gap becomes smaller, and not larger...) and how to plot them in Matlab. Any help appreciated.

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Jan 2018-2-26

Can you post an example of what you mean? A screen shot or picture?

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Answer 1

Star Strider 2018-2-26

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https://ww2.mathworks.cn/matlabcentral/answers/384950-how-to-get-the-ticks-for-each-value-of-the-logarithmic-scale#answer_307229

在 MATLAB Online 中打开

The ticks between 10^0 (or 1) and 10^1 (or 10) are the integers between 1 and 10. They are scaled logarithmically, so the apparent distance between them appears to decrease.

This example code:

x = linspace(0.1, 1.0, 10);
y = x;
figure(1)
semilogx(x, y)
ax = gca;
ax.XMinorTick = 'on';
ax.XAxis.TickValues = x;
ax.XAxis.Exponent = 1;
xlabel('Logarithmic X-Axis')
ylabel('Linear Y-Axis')
title('Illustrating Logarithmic Scaling')

produces this plot:

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Tahariet Sharon 2018-2-26

Thanks. I still don't understand why there is a bigger gap from 10Hz to 20 Hz than from 70Hz to 80Hz.

Star Strider 2018-2-26

在 MATLAB Online 中打开

My pleasure.

The decreasing gaps are due to plotting logarithmic values on a linear scale (which is what the semilog axis does).

Consider:

Xtix = log10(10:10:100)
DiffXTix = diff([0 Xtix])
Xtix = 1.0000    1.3010    1.4771    1.6021    1.6990    1.7782    1.8451    1.9031    1.9542    2.0000
DiffXTix = 1.0000    0.3010    0.1761    0.1249    0.0969    0.0792    0.0669    0.0580    0.0512    0.0458

You can see that the differences between the logarithm values decrease as the values themselves increase. That is the nature of logarithms, and what the plot illustrates.

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