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Exponential growth curve-fitting

Exponential growth curve-fitting

Exponential growth curve-fitting

(OP)
Hi, i have got a bunch of data points, which i want a curve fitted to. The function for the curve is y= b*a^x . Now, i have tried genfit and expfit, but they find coeffs for y=a*e^(b*x) and y=b*x^b. How do get the coeffs for y= b*a^x?

RE: Exponential growth curve-fitting

I think genfit works.  Can you list the elements of your function vector?

RE: Exponential growth curve-fitting

(OP)
well i didnt really know what elements to put in, can u help?

RE: Exponential growth curve-fitting

The first element of the function vector is the form of your solution:  u1*u2^x,  where u1 and u2 are two elemnts of an array

The second element is the first derivative of the first element with respect to the first variable:  u2^x

The third element is the first derivative of the first element with respect to the second variable:  u1*x*u2^x-1

Here's how the function vector looks.  I included the "[" below as that's what you type to get the subscript.  The "T" at the end denotes a transposed array.

F(x,u)=(u[1*(u[2)^x   (u[2)^x    u[1*x*(u[2)^x-1))T
p=genfit(vx,vy,g2,F)
vx and vy are your data point vectors
g2 is a two element guess

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