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Re: surface fit [message #3150 is a reply to message #3059]

Wed, 09 November 1994 05:53

thompson
Messages: 584
Registered: August 1991

Senior Member

buteau@bali.saclay.cea.fr (A.Buteau 62 17) writes:

> I don't understand what you mean by :

>> One then is not fitting F(X,Y) but F(S). All one needs to do then is to
>> write the definition of the function so that it can then determine X(S) and
>> Y(S). A simple way to do this is through a common block.

O.K., here's a simple example. Suppose that one wanted to fit a
two-dimensional gaussian to a set of X-Y points, i.e.

F(X,Y) = A0 + A1*exp(-r^2/(2*sigma^2))

r^2 = (x-X0)^2 + (y-y0)^2

One would then write the function as follows:

FUNCTION GAUSS2, S, A, PDER
COMMON GAUSS2_COM, X_ARRAY, Y_ARRAY
X = X_ARRAY(S)
Y = Y_ARRAY(S)
R2 = (X - A(2))^2 + (Y - A(3))^2
F = A(0) + A1*EXP(-R2/(2.*A(4)^2))
PDER = ... ;Left as an exercise to the reader :^)
RETURN, F
END

Your actual measurement points are a series of X,Y pairs. These are stored as
X_ARRAY, Y_ARRAY in the GAUSS2_COM common block. S is simply an index array
running from 0 to one less than the number of points. If the measured values
at these points are Z, then one can call CURVEFIT as follows

Result = CURVEFIT(S, Z, W, A, SIGMAA, FUNCTION='GAUSS2')

Bill Thompson

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[Message index]

		Surface fit or 3d interpolation By: paz on Mon, 22 November 1993 10:29
		Re: surface fit By: buteau on Tue, 08 November 1994 08:12
		Re: surface fit By: thompson on Wed, 09 November 1994 05:53

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