comp.lang.idl-pvwave archive: archive » curve fitting: works badly?

Home » Public Forums » archive » curve fitting: works badly?

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: curve fitting: works badly? [message #3676 is a reply to message #3672]

Mon, 06 March 1995 15:49

thompson
Messages: 584
Registered: August 1991

Senior Member

feil@prl.philips.nl (Hans Feil) writes:

> I try to use CURVEFIT to get some simple data fitted to an harmonic
> oscillator.

> Somehow things don't work very good.

(stuff deleted)

> pro FUNCT,x,a,f,pder

> f = a(0) + a(1)*(x-a(2))^2

> PDER = FLTARR(N_ELEMENTS(X),3) ;YES, MAKE ARRAY.
>
> PDER(*,0) = 1.0 ;COMPUTE PARTIALS
> PDER(*,1) = (x-a(2))^2
> PDER(*,2) = 2*a(1)*(x-a(2))
^^^^^^^^^^^^^^^
> end

> RETURN

> end

I think that your problem is here. I believe that the sign of this partial
derivative should be negative.

I've often had this problem with this technique. If the partial derivatives
are calculated wrong, you can compute till doomsday and it'll never converge.
I often just don't bother to try to figure it out anymore, and just do the
derivatives numerically.

Bill Thompson

Report message to a moderator

[Message index]

		curve fitting: works badly? By: feil on Mon, 06 March 1995 08:19
		Re: curve fitting: works badly? By: thompson on Mon, 06 March 1995 15:49
		Re: curve fitting: works badly? By: swalton on Tue, 14 March 1995 11:16

Previous Topic:	Re: New User seeks book
Next Topic:	widget_button

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Sun Nov 30 14:16:02 PST 2025

Total time taken to generate the page: 1.76261 seconds