Y = a*exp(b*x)+c*exp(d*x) formulas

Hello,

Do you have some idea where I can find more info regarding this type of exponential model Y = a*exp(b*x)+c*exp(d*x)?

I need to know more about the inner math inside it. So far the books about numerical methods that I've looked into haven't got something useful.

Any hint will be useful, thanks in advance!

[Walter Roberson]

What kind of information are you looking for? It appears to be just the sum of two exponentials.

[the cyclist]

If you are trying to fit data to a functional form like that, you might investigate the function nlmefit() in the Statistics Toolbox.

Answer 1

[Viorel]

@Walter Roberson Thanks for your reply @the cyclist, the function presented does the trick, I just must find the mathematics involved in it.

Yes it's just a sum, but makes things complicated. If it was just an exponential, the math should be:

y=a*e^b*x

then make things linear through logarithm

ln(y)=ln(a)+b*x

some things regarding least squares, partial derivative and... over

This sum is making me crazy, it looks like I need a nonlinear curve fitting, but I need some more info regarding solving this kind of problem.

PS. weird, the forum didn't send any email about the answers, sorry for my delay.

[Walter Roberson]

There isn't always a robust theory behind solving such systems: sometimes it just needs a numeric approach.