;+
; pro mcosfunct, X, A, F, pder
;
; Purpose: Cosine Function (Reverse)
; 
; Input: X
;        A: Coef. A[0]: Magnitude A[1]: Constant
;
; Output: F
; 
; Initial version: Yi-Jiun Su, AFRL, 2012/11/09
;
;-
pro mcosfunct, X, A, F, pder 
  mx = max(X,/NaN)
  bx = -1.*COS(X*2.*!pi/mx)
  F = A[0]*bx+A[1]
  if N_PARAMS() ge 4 then begin
    cx = SIN(X*2.*!pi/mx)
    pder = [[bx],[A[0]*cx]]
  endif
end