MATLAB: How to use fit in logY

fitlogystraight line

Hi Does anybody knows how to use fit in log(Y). I mean I have x and y data, I am plotting it and fitting points by straight line using matlab toolbox. When I take log in Y axis my straight fit line becomes curve line. I want straight line fit not curve fit.

How I can get straight fit line in log y plot?

Any advice appreciated.

Best Answer

A line which is straight in a linear plot will always be curved in a log plot...? If you want it to be straight in a log10 plot, your original fit has to be exponential 10^x.

What you can do is e.g. get a linear fit g(x) to log10(y), and then f(x) = 10.^g(x) will be your actual regression function (which is obviously exponential).

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Your x starts from 0 (and is one point longer than y1 or y2.) If you set the axis XScale to log, then you are attempting to take log(0), which leads to problems in drawing the patch.

Without the 0 I had no problem.

x = 1:100;
y1 = rand(1,100)+1.5;
y2 = rand(1,100)+0.5;
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pause(3)
set(gca,'XScale','log','YScale','log')
drawnow()

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