FUNCTION funz,a,b,X,Y
SZ=SIZE(X)
N=SZ[1] & M=SZ[2]
RETURN,COS(2*!PI*(a*X/N+b*Y/M))
END


PRO COS_ARRAY,N,M,T,W,U,V,R
;+
;COS_ARRAY,N,M,A,W,U,V,R constructs NxM array A containing
;the functions
;fab(x,y)=cos(2*pi*(ax/N+by/M)) as rows for
;a over the range 0,1,2...N-1 and
;b over the range 0,1,2,...M-1. The SVD of A is then
;calculated and returned in W,U,V. The rank R
;is computed by the number of singular values
;that are greater than 1e-5
;See SVDC.
;
;H. Rhody, July, 2000
;-

meshdom,findgen(N),findgen(M),X,Y
T=FLTARR(N*M,N*M)
k=0
FOR a=0,N-1 DO BEGIN
  FOR b=0,M-1 DO BEGIN
    z=funz(a,b,x,y)
  	T[*,k]=z[*]
  	k=k+1
ENDFOR
ENDFOR
SVDC,T,W,U,V
R=TOTAL(ABS(W) ge 1E-5)
END