NAME: 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 SIDE EFFECTS: NONE. RESTRICTIONS: 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 ()