How do I extract the exponent from a semilogy plot?

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Janna Hinchliff
Janna Hinchliff 2019-2-26
评论： Stephan 2019-2-26
If I use semilogy to plot some data such that the plot appears as a straight line, how can I extract the exponent of this line? Can I use polyfit to get this or is there a different way?

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Stephan
Stephan 2019-2-26
编辑：Stephan 2019-2-26
Hi,
i think you should use lsqcurvefit (requires Optimization Toolbox) or fit (requires Curve Fitting Toolbox) - depending on the toolboxes you have access to. I would expect an exponential function if there is a straight line in the semilogy plot. Due to this polyfit is not the correct choice. I recommend to work through this examples:
lsqcurvefit:
https://de.mathworks.com/help/optim/ug/lsqcurvefit.html#buuu2mv-1
fit:
https://de.mathworks.com/help/curvefit/fit.html#bto2vuv-9
In case of lsqcurvefit the resulting elements of solutiuon x contain the needed exponent. In case of fit you get the values with the coeffvalues function.Therefore see also Fit Postprocessing.
Best regards
Stephan
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Janna Hinchliff
Janna Hinchliff 2019-2-26
No worries, I sorted it - I had another variable stored as fit from a different part of the code! Thanks for your help!
Stephan
Stephan 2019-2-26
No problem - if this was useful for you please accept my answer.

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