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PLCH_FUN

plch_fun

## Purpose

Two 2-d gaussian images, support routine for PLCHFIT.

## Description

Evaluate the sum of two 2-d guassian and a 2-d 2nd order polynomial
and optionally return the value of it's partial derivatives.
Evaluate the equation y=f(i) where:
X = I MOD NX
Y = I / NX
R1 = SQRT( (X-A0)^2 + (Y-A1)^2 )
R2 = SQRT( (X-A0-A6)^2 + (Y-A1-A7)^2 )
Z1 = R1/A3
Z2 = R2/A3
F(I) = A2*EXP(-Z1^2/2) + A5*EXP(-Z2^2/2) + A4
Function parameters
--------------------------------------------
A0 = X location of center of Pluto
A1 = Y location of center of Pluto
A2 = height of gaussian for Pluto
A3 = the 1/e width of the guassian
A4 = Constant term for the background
A5 = height of gaussian for Charon
A6 = X location of center of Charon relative to Pluto
A7 = Y location of center of Charon relative to Pluto

## Category

Function fitting

## Calling Sequence

FUNCT,I,A,F[,PDER]

## Inputs

I = Independent variable, actually, just an index into 2-d array.
A = PARAMETERS OF EQUATION DESCRIBED BELOW.
OPTIONAL KEYWORD PARAMETERS:
XSIZE = width of image

## Outputs

F = value of function at each F(I).

## Optional Output Parameters

PDER = (N_ELEMENTS(I),8 or 6) array containing the
partial derivatives. P(I,J) = Derivative
at Ith point w/respect to Jth parameter.

## Common Blocks

r2gauss_com - contains the x-width of the array stored in A

NONE.

NONE.

## Modification History

Written by Marc W. Buie, Lowell Observatory, 1993 January 13
93/07/01, MWB, changed to remove linear and quadratic background
terms, added facility for forcing position of Charon.
2000/11/08, MWB, removed use of obsolete ()

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