Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/~mperrin/software/sources/gaussian2d.pro Дата изменения: Fri Dec 2 06:17:42 2005 Дата индексирования: Sat Mar 1 15:44:29 2014 Кодировка: Поисковые слова: http www.badastronomy.com phpbb index.php

function gaussian2d, xi1, xi2, parms, pderiv, DOUBLE=double
;+
; NAME:
; GAUSSIAN2d
; PURPOSE:
; Compute the 2-d Gaussian function and optionally the derivative
;
; based on Goddard IDL Astro's "Gaussian.pro"
;
; RESTRICTION: Right now only circularly symmetric gaussians
;
; EXPLANATION:
; Compute the 2-D Gaussian function and optionally the derivative
; at an array of points.
;
; CALLING SEQUENCE:
; y = gaussian( x, y, parms,[ pderiv ])
;
; INPUTS:
; x,y = arrays, independent variable of Gaussian function.
;
; parms = parameters of Gaussian, 2, 3 or 4 element array:
; parms[0] = maximum value (factor) of Gaussian,
; parms[1] = mean value (center) of Gaussian in X,
; parms[2] = mean value (center) of Gaussian in Y,
; parms[3] = standard deviation (sigma) of Gaussian.
; (if parms has only 2 elements then sigma taken from previous
; call to gaussian(), which is stored in a common block).
; parms[4] = optional, constant offset added to Gaussian.
; OUTPUT:
; y - Function returns array of Gaussian evaluated at xi. Values will
; be floating pt. (even if xi is double) unless the /DOUBLE keyword
; is set.
;
; OPTIONAL INPUT:
; /DOUBLE - set this keyword to return double precision for both
; the function values and (optionally) the partial derivatives.
; OPTIONAL OUTPUT:
; pderiv = [N,3] or [N,4] output array of partial derivatives,
; computed only if parameter is present in call.
;
; pderiv[*,i] = partial derivative at all xi absisca values
; with respect to parms[i], i=0,1,2,[3].
;
;
; EXAMPLE:
; Evaulate a Gaussian centered at x=0, with sigma=1, and a peak value
; of 10 at the points 0.5 and 1.5. Also compute the derivative
;
; IDL> f = gaussian( [0.5,1.5], [10,0,1], DERIV )
; ==> f= [8.825,3.25]. DERIV will be a 2 x 3 array containing the
; numerical derivative at the two points with respect to the 3 parameters.
;
; COMMON BLOCKS:
; gaussian ; why is this here??
; HISTORY:
; 2005-May-06 Forked from gaussian.pro by Marshall Perrin
;
;-
On_error,2
common gaussian, sigma

if N_params() LT 2 then begin
print,'Syntax - y = GAUSSIAN( xi, parms,[ pderiv, /DOUBLE ])'
print,' parms[0] = maximum value (factor) of Gaussian'
print,' parms[1] = mean value (center) of Gaussian'
print,' parms[2] = standard deviation (sigma) of Gaussian'
print,' parms[3] = optional constant to be added to Gaussian'
return, -1
endif

common gaussian, sigma

Nparmg = N_elements( parms )
npts1 = N_elements(xi1)
npts2 = N_elements(xi2)
ptype = size(parms,/type)
if (ptype LE 3) or (ptype GE 12) then parms = float(parms)
if (Nparmg GE 4) then sigma = parms[3]

double = keyword_set(DOUBLE)
if double then $ ;Double precision?
gauss = dblarr( npts1,npts2 ) else $
gauss = fltarr( npts1,npts2 )

xx = rebin(xi1-parms[1],npts1,npts2)
yy = rebin(reform(xi2-parms[2],1,npts2),npts1,npts2)
xi = sqrt(xx^2+yy^2)

z = ( xi )/sigma
zz = z*z

; Get smallest value expressible on computer. Set lower values to 0 to avoid
; floating underflow
minexp = alog((machar(DOUBLE=double)).xmin)

w = where( zz LT -2*minexp, nw )
if (nw GT 0) then gauss[w] = exp( -zz[w] / 2 )

; TODO make the following work in 2D
if N_params() GE 4 then begin

if double then $
pderiv = dblarr( npts1, npts2, Nparmg ) else $
pderiv = fltarr( npts1, npts2, Nparmg )
fsig = parms[0] / sigma

pderiv[0,0] = gauss
pderiv[0,1] = gauss * z * fsig

if (Nparmg GE 3) then pderiv[0,2] = gauss * zz * fsig
if (Nparmg GE 4) then pderiv[0,3] = replicate(1, npts)
endif

if Nparmg LT 5 then return, parms[0] * gauss else $
return, parms[0] * gauss + parms[4]
end