Has anyone come across with the following:

I need to calculate parameters  a1, n1 ... a3, n3 of the following equation (linear, say):

a1, a2, a3 are coefficients;
n1, n2, n3 are exponential ones.


Y = X1 (a1 * V^{n1} + a2 * V^{n2} + a3 * V^{n3})

where Y, X1, and V are known values.

Will it be possible to do so in MATLAB?  if so, I would highly appreciate if you could let me know the procedure.

Else, any other approach will be warmly welcomed.

Thx in advance.

Do "lookfor parameter".
Looks like something which should be done in matlab.
If you can linearize that equation and change into matrix form, that could be one way.

I think you need the Curve Fitting Toolbox, or may be try statistical model fitting in JMP or Minitab

Aiya!!!

This is a linear combination of exponential functions! I wonder if the fminsearch function will come in handy. I've never used it though.

You'll have to set up your function as follows:

Y = X1 (a1 * V^{n1} + a2 * V^{n2} + a3 * V^{n3})

Let P=Y./X1;

So now you'll have:

P=a1*V^{n1} + a2*V^{n2}+a3*V^{n3};

Beyond that, I can't say much.

If you could provide the scenario in which you're trying to estimate this, perhaps it would help?

It would still be degenerate, I think.

More detail might help.

Yeap, I thought the same, f22.
Either CFT or system identification approach might work.

Is any one using Siemens PTI PSS/E tool for power systems dynamic simulation??

--

thx guys for your inputs.

Try least square. Here is a nonlinear solver

help lsqnonlin
 LSQNONLIN solves non-linear least squares problems.
    LSQNONLIN attempts to solve problems of the form:
    min  sum {FUN(X).^2}    where X and the values returned by FUN can be  
              x             vectors or matrices.

choose FUN = Y - X1 (a1 * V^{n1} + a2 * V^{n2} + a3 * V^{n3}) and put known constants Y, X1 and V. The x vectors would be [a1, a2, a3, n1, n2, n3]. It will find the least square i.e. FUN^2 for different possible of x. Minimum FUN^2 will be 0 so you will get Y = X1 (a1 * V^{n1} + a2 * V^ + {n2}a3 * V^{n3}) by changing a's and n's.

.
Thx nepaliraja for the valuable info.  (sorry for the late response).

I used "polyfit" to calculate the coefficients and keeping it 3rd degree polynomial. Meanwhile,
this is working.

Cheers !

Happy Dashain to you all Sajha friends.