SFIT

The SFIT function determines a polynomial fit to a surface and returns a fitted array. The function fitted is:

This routine is written in the IDL language. Its source code can be found in the file sfit.pro in the lib subdirectory of the IDL distribution.

Syntax

Arguments

Data

The two-dimensional array of data to fit. The sizes of the dimensions may be unequal.

Degree

Keywords

Set this keyword to a named variable that will contain the array of coefficients for a polynomial function of x and y to fit data. This parameter is returned as a Degree+1 by Degree+1 array.

Examples

; Create a grid from zero to six radians in the X and Y directions: 
X = (FINDGEN(61)/10) # REPLICATE(1,61) 
Y = TRANSPOSE(X) 
 
; Evaluate a function at each point: 
F = -SIN(2*X) + COS(Y/2) 
 
; Compute a sixth-degree polynomial fit to the function data: 
result = SFIT(F, 6) 
 
; Display the original function on the left and the fitted function 
; on the right, using identical axis scaling: 
WINDOW, XSIZE = 800, YSIZE = 400 
 
; Set up side-by-side plots: 
 
!P.MULTI = [0, 2, 1] 
 
; Set background color to white: 
 
!P.BACKGROUND = 255 
 
; Set plot color to black: 
 
!P.COLOR = 0 
 
SURFACE, F, X, Y, ZRANGE = [-3, 3], ZSTYLE = 1 
SURFACE, result, X, Y

The following figure shows the result of this example. The original function is on the left and the fitted function is on the right: