# How to best fit a curve to my data

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Iddo Weiner il 5 Dic 2017
Commentato: Iddo Weiner il 5 Dic 2017
Hi, I have 2 variables (attached in the file myXY.mat) to which I would like to fit a curve.
I'm expecting to receive something like this (the pic is manually drawn):
Here's my code:
f = fit(X,Y,'exp1')
plot(f,X,Y)
And here's what I get:
Any ideas what the code should be to receive a fit more similar to what I drew?
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Geoff Hayes il 5 Dic 2017
Iddo - have you tried a polynomial fit instead? i.e. poly2 or poly3?
Iddo Weiner il 5 Dic 2017
Hi, I tried it now, but it doesn't really get any better.
What actually is working for me now is a function called sigm_fit which I found in the file exchange:
https://www.mathworks.com/matlabcentral/fileexchange/42641-sigm-fit
• But I would still like to know if there's a "native" MATLAB solution for this..
Thanks

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### Risposta accettata

Matt J il 5 Dic 2017
f=fit(X,Y,'power2')
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Iddo Weiner il 5 Dic 2017
thanks

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### Più risposte (1)

Rik il 5 Dic 2017
You need to change the starting guesses and you might have to adjust the function itself.
x=0:0.01:10;
y=1-exp(-x);
plot(x,y)
The code above will result in a similar shape of what you are asking. 'exp1' will support this, except for the offset. You can provide your own function instead by using the anonymous function input.
PS you need to make sure that for your application, it is indeed an exponential function and not a (square) root.
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