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Problem with Power Regression

Asked by Akhmad Muktaf on 19 Jul 2019
Latest activity Commented on by the cyclist
on 20 Jul 2019
I have a coding to develop a formula using power regreesion
Here my coding:
plot(Xbin,Ybin,'+r'), hold on
p = polyfit(log(Xbin),log(Ybin),2);
m = p(1);
b = exp(p(2));
ezplot(@(x) b*Xbin.^m,[Xbin(1) Xbin(end)])
Error in Power_Regression (line 242)
ezplot(@(x) b*Xbin.^m,[Xbin(1) Xbin(end)])
I appreciate the help
Akhmad

  2 Comments

Image Analyst
on 19 Jul 2019
Why not use fitnlm() for a better fit? I'm attaching several examples. Would you consider that (fitnlm) instead of taking the log and doing polyfit() on the logged data?
Dear Cyclist,
I tried to follow your suggestion, but every coding ask about function table can you explain this?

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1 Answer

Answer by the cyclist
on 19 Jul 2019
Edited by the cyclist
on 19 Jul 2019
 Accepted Answer

polyfit(...,2) is fitting a constant, linear, and quadratic term. Notice that the output vector p has three elements. You want this instead:
% Some made-up data
Xbin = (1:10)';
Ybin = 2 * Xbin.^3 + 0.07*randn(10,1);
figure
plot(Xbin,Ybin,'+r'), hold on
p = polyfit(log(Xbin),log(Ybin),1);
m = p(1);
b = exp(p(2));
ezplot(@(x) b*x.^m,[Xbin(1) Xbin(end)])
I also corrected the fact that you used @(Xbin) instead of @(x) in the function definition.
[Sorry if you saw some of the intermediate edits I did, before I realized the true source of your problem.]

  2 Comments

Thank you, my coding is working know. I want to know how to write the euation and R square inside the figure?
Thank you
Akhmad
the cyclist
on 20 Jul 2019
Try the annotation command.
You could also use the text command, but annotation is more powerful, and handy to learn.

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