OK I thought this would be very easy, but after much puzzling I still can not figure this out.

Let's say that I start with some explicit floating-point numbers:

a_num := 1.330 :
b_num := 2.440 :
c_num := 3.660 :

The I construct a function using these values:

func := ( a_num + b_num * x ) * exp( - c_num * x ) :

Now what I need to do is simply the opposite of this: given the function func, and given an explicit known form of the function, assign the values a, b, c. Hypothetically it would look something like this: