How to curve fit an equation with sigma function

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Dear all,
I would like to get coefficient C0, C1....CN from the below equation,
function.JPG
I have enclosed herewith an excel having x and y co-ordinates.
Can anybody please let me know how to write this equation in 'custom equation' option in curve fitting tool or is there any other way to do it?

Answers (2)

Alex Sha
Alex Sha on 27 Jul 2019
Hi, where are the values of Z?
  1 Comment
Gaurav Nanajkar
Gaurav Nanajkar on 27 Jul 2019
Hi Alex, I saw the details of the equation and according to that this equation is for 'rotationally symmetric polynomial'. As I am using it for 2D curve, in my case Z value will be 0

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Catalytic
Catalytic on 27 Jul 2019
C = polyfit( sqrt( x.^2+y.^2) , Z, N)
  4 Comments
Matt J
Matt J on 29 Jul 2019
Edited: Matt J on 29 Jul 2019
As you mentioned as its a higher order polynomial I will not use polyfit due to higher perecentage error.
No, that is not what I said. What I said was "It's not that polyfit is better or worse at fitting high order polynomials. It's just that high order polynomials are typically a bad thing...".
Stop using high order polynomials. Use splines instead.

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