Problem with Power Regression

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

[Image Analyst]

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?

[Skydriver]

Dear Cyclist,

I tried to follow your suggestion, but every coding ask about function table can you explain this?

Answer 1

[the cyclist]

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.]

[Skydriver]

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]

Try the annotation command.

You could also use the text command, but annotation is more powerful, and handy to learn.