How to add Levenberg Marquardt.vi's input port?

[xuelang8]

ChrisJ
it's a good idea, I'll try it,Thanks.

[altenbach]

After some private conversations, it turns out that x(t) is a sinusoidal function and y(t) is it's first derivative.

To be fit is the function z(t)=(a+b*x+c*x^2+d*x^3+e*x^4)*y+A*x*exp(B*x)

I have quickly implemented the above ideas and made a demo VI using simulated data with noise. It converges very fast from all zero parameters estimates and seems very stable. I am sure many improvements are possible.

[xuelang8]

Thanks altenbach for his detailed reply and self-giving help!!!!