Hi,
As
Sean correctly pointed out, if you know the model and want to find model parameters for it, then
FindFit[] is for you.
Here is an example:
(* test function *)
f[x_] := 5. Exp[-0.98 x] + 3. Exp[-1.34 x];
(* plot it *)
Plot[f[x], {x, 0, 3}, PlotRange -> All]
(* data *)
data = Table[{x, f[x]}, {x, 0, 3, 0.01}];
(* find fit *)
FindFit[data, a Exp[b x] + d Exp[c x], {a, b, c, d}, x]
I.M.