Curve Fit of ODE, should I use Lev-Mar or Constrained Nonlinear Optimization?

[myafu]

I wanna do a curve fitting of differential equations, following is the equations:

dx/dt = u*x-a*x
ds/dt = b*u*x+c*x
dp/dt = d*u*x+e*x+f*p

and u = um*s/(km+s+s^2/ki)

I've tried "nonlinear curve fit( Lev-Mar)", but I met difficulties when writing the f(x,a) of Lev-Mar.
Then I tried "Constrained Nonlinear Optimization", I found that the example "Estimate Nonlinear Spring Constant.vi"
in the "labview\examples\math\curvefit.llb" was similar to the fitting I tried to do, but there was only one parameter
need to estimate in this example,but what I need is to estimate 3 parameters.
However,I modified the example to my equations, it failed again.

How can I achieve this? is it possible to do this fit only using Labview VIs or need Matlab Script Node?

Any help will be appreciated.

[myafu]

I forgot to mention that in the equations above,  a,b,c,d,e,f is constant,
and the data of x,s,p corresponding with the data of time is already known,
and which parameters I wanna identify is um,km,and ki

帖子被myafu在12-22-2006 01:33 AM时编辑过了

[buckidge]

have you had any luck with this?
I'm working with a similar type of problem and am curious as to what you came up with, if anything....

BTW... I'm using the LM-bound curve fit but was curious about minimizing Chi-square between a generated curve and the measured curve using nonlineear optimization.

-nick