How to fit this eqation:y=a-b+*c^x ?

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afrya
afrya 2013-12-13
评论： Image Analyst 2013-12-13
Hi,
I am wondering how can I fit the following equation: y=a-b+*c^x since it is not included in the library and how can I exclude some point without using the curve fitting toolbox. When I use the following expression,I receive an error message
g = fittype('a-b*c^x','coeff',{'a','b','c'})
[curve2,gof2] = fit(y2,Av,g)
Thank you in advance
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afrya
afrya 2013-12-13
a, b, and c are all coefficients
Image Analyst
Image Analyst 2013-12-13
Looking more closely I think that you meant b to be a multiplicative factor, not a scalar that you subtract and that you just made a mistake when you wrote "y=a-b+*c^x". Because of what Roger said, and you said later, I think what you really meant was y=a-b*c^x and you just put in the + sign by mistake.

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回答（1 个）

Roger Stafford
Roger Stafford 2013-12-13
Instead of 'a-b*c^x' you might try the equivalent 'a-b*exp(k*x)'. If you can fit to that, then c = exp(k) will be a fit for 'a-b*c^x'.

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