Thread Subject: Multivariate polynomial approximation

Hi,

I have a highly nonlinear function depending on several
variables, i.e. y=f(x1,x2,...,xn). I would like to
approximate it numerically with a multivariate polynomial
such that:

y = sum_i (ai*x1^(b1)*...*xn^(bn))

Is there exists a matlab function which may perform this
approximation?

Best regards,
V. Morio

"Vincent Morio" <vincent.morio@mathworks.com> wrote in message
<fsli3g$3fj$1@fred.mathworks.com>...
> Hi,
>
> I have a highly nonlinear function depending on several
> variables, i.e. y=f(x1,x2,...,xn). I would like to
> approximate it numerically with a multivariate polynomial
> such that:
>
> y = sum_i (ai*x1^(b1)*...*xn^(bn))
>
> Is there exists a matlab function which may perform this
> approximation?

polyfitn

http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?
objectId=10065&objectType=FILE

HTH,
John

"John D'Errico" <woodchips@rochester.rr.com> wrote in
message <fslldq$3i$1@fred.mathworks.com>...
> "Vincent Morio" <vincent.morio@mathworks.com> wrote in
message
> <fsli3g$3fj$1@fred.mathworks.com>...
> > Hi,
> >
> > I have a highly nonlinear function depending on several
> > variables, i.e. y=f(x1,x2,...,xn). I would like to
> > approximate it numerically with a multivariate polynomial
> > such that:
> >
> > y = sum_i (ai*x1^(b1)*...*xn^(bn))
> >
> > Is there exists a matlab function which may perform this
> > approximation?
>
> polyfitn
>
>
http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?
> objectId=10065&objectType=FILE
>
> HTH,
> John

Thank you John. Your function polyfitn works very well!!
Vincent