Setting your own start points for curve fitting

I have a set of data which I am attempting to fit via a modified ("custom") two-exponential function: a*exp(b*(x-x0))+c*exp(d*(x-x0))+y0, where x0 and y0 are known. I know how to set upper and lower bounds for a,b,c,d, but how can I specify starting values (start points) for them?

Thanks in advance.

[J.S.]

I actually meant syntax-wise. I know what values I would like to use as start points, but how can I implement them in my code?

[Adam Danz]

I see, what function are you using to do the fitting? For most of matlab's fitting functions, the 2nd input is "x0" which is a vector of values [1-by-n] for the n parameters of the function you're fitting. If the parameters in your function are [a,b,c,d] with an expected outcome of [100, 20, .5, -2], then that vector would be the input to 'x0'.

[J.S.]

I am using my custom two-exponential with x and y offsets: a*exp(b*(x-x0))+c*exp(d*(x-x0))+y0, where x0 and y0 are known.

Answer 1

[Walter Roberson]

If you are using fit() then use the InitialPoint option as shown in https://www.mathworks.com/help/curvefit/fit.html#bto2vuv-10