Constrained data fit routine

[Labview user1]

Is there a vi routine that perfoms a constrained fit on xy data.
e.g. Find the "positive" coefficients for a 2nd order polynomial.
y= a + bx + cx^2
where: a, b, and c are only positive

[e-Cash-Money]

Hello LabVIEW user1,

There is no vi routine that will perform that specific operation or any other constraints as far as I can find. Here is a link to another dicusssion forum post on the same issue. If this does not address your question, please let me know and we can talk about it some more!

http://forums.ni.com/ni/board/message?board.id=170&message.id=59840&requireLogin=False

Thanks,
E.Lee
Applications Engineer
National Instruments

[altenbach]

You can always re-parameterize your problem such that you can fit an unconstrained derived parameter using Lev_Mar routines.

Some ideas for constraining are given for example in this link. (Look for "One-sided boundary constraints").

In your case, you could fit for y= a1^2 + b1^2x + c1^2x^2 in which a1, b1, and c1 are unconstrained, then calculate a=a1^2 ,b=b1^2, and c=c1^2 at the end.

[Labview user1]

Thank you very much! This routine will get me there.