# How to curve fit an equation with sigma function

조회 수: 6(최근 30일)
Gaurav Nanajkar 2019년 7월 25일
편집: Matt J 2019년 7월 29일
Dear all,
I would like to get coefficient C0, C1....CN from the below equation,
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?

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### 답변(2개)

Alex Sha 2019년 7월 27일
Hi, where are the values of Z?
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Gaurav Nanajkar 2019년 7월 27일
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 2019년 7월 27일
C = polyfit( sqrt( x.^2+y.^2) , Z, N)
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Matt J 2019년 7월 29일
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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