Mathematica FindFit - proper format question

Hi everyone,

Thanks in advance for your help. I'm trying to fit a system of coupled ODEs to some experimental data; currently executing my code results in the function returning itself. The documentation claims this means that there is no syntax errors but Mathematica doesn't know what to do with my input (i.e. I'm doing something wrong, but it isn't blatant to Mathematica).

I'm new to Mathematica so without errors to guide me (and without finding anything helpful on the web), I'm at a loss.

The system of ODEs is somewhat complicated, so here is a simple example that does the same thing:

Code:

`system={y1'[t]==A,y2'[t]==B};`

pars={A,B};

vars={y1[t],y2[t]};

expvalues={{0,0,0},{1,5,10},{2,10,Null}};

FindFit[expvalues,system,pars,vars]

Obviously this is a trivial example; I'm trying to fit y1=A*y1 and y2=B*y2 to some sample data where A=5 and B=10.

I put "Null" in to the second set of experimental values because in my actual system I have some blanks in my experimental values (e.g. at time=10 I have input for 3 of the 5 variables, and at time=20 I have input for a different 3 of the 5 variables). I'm not sure if that is the correct way to put an "empty" value in to the list (and it does seem that you have to have something for each variable at each time point you're giving data), but if you replace the Null with a "20" in the code you get the same error, so that isn't the only issue with what I've done.

Thanks again!