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Re: GAUSS_FUNCT problem [message #38224]

Fri, 27 February 2004 10:37

Wayne Landsman
Messages: 117
Registered: January 1997

Senior Member

> PRO GAUSS_FUNCT,X,A,F,PDER
> COMPILE_OPT idl2, hidden
> ON_ERROR,2 ;Return to caller if an error occurs
> n = n_elements(a)
> if a[2] ne 0.0 then begin
> Z = (X-A[1])/A[2] ;GET Z
> EZ = EXP(-Z^2/2.) ;GAUSSIAN PART
> endif else begin
> z = 100.
> ez = 0.0
> endelse
>
> case n of
> 3: F = A[0]*EZ
> 4: F = A[0]*EZ + A[3]
> 5: F = A[0]*EZ + A[3] + A[4]*X
> 6: F = A[0]*EZ + A[3] + A[4]*X + A[5]*X^2 ;FUNCTIONS.
> ENDCASE
>

> Of course, the "fix" to this is to make Z an array of N elements with
> each element set to 100 and EZ an array of N elements with each element
> set to 0 in the case where A[2] is equal to 0. This ensures that F is
> always an array.

Well, I can half-heartedly defend the existing code. Note that if one
supplies 5 or 6 terms (linear or quadratic background) then GAUSS_FUNCT
properly returns an array when A[2] = 0. In the case of 3 terms you
are computing a function which only consists of a Gaussian with a sigma
width of 0, which probably indicates that you have made an earlier
mistake. So I don't begrudge GAUSS_FUNCT returning an anomalous result.

But yes, I agree that EZ should be set to an zero array of N elements in
case A[2] = 0 (though it should probably be set to NaN wherever X = A[1] ).

--Wayne Landsman

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		Re: GAUSS_FUNCT problem By: Wayne Landsman on Fri, 27 February 2004 10:37
		Re: GAUSS_FUNCT problem By: David Fanning on Fri, 27 February 2004 09:24
		Re: GAUSS_FUNCT problem By: Michael Wallace on Sun, 29 February 2004 18:23

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