How to curve fit an equation with sigma function

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Gaurav Nanajkar
Gaurav Nanajkar el 25 de Jul. de 2019
Editada: Matt J el 29 de Jul. de 2019
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?

Respuestas (2)

Alex Sha
Alex Sha el 27 de Jul. de 2019
Hi, where are the values of Z?
  1 comentario
Gaurav Nanajkar
Gaurav Nanajkar el 27 de Jul. de 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 el 27 de Jul. de 2019
C = polyfit( sqrt( x.^2+y.^2) , Z, N)
  4 comentarios
Gaurav Nanajkar
Gaurav Nanajkar el 28 de Jul. de 2019
ok thanks for the clarification Matt. As you mentioned as its a higher order polynomial I will not use polyfit due to higher perecentage error.
Can you please let me know the way to curve fit it as I am not getting how to use in curve fitting app custom function due to sigma?
Matt J
Matt J el 29 de Jul. de 2019
Editada: Matt J el 29 de Jul. de 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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