DEFINITION MODULE FourNM;

  (* EXPORT QUALIFIED FourN; *)

   FROM NRVect  IMPORT Vector;
   FROM NRIVect IMPORT IVector;

   PROCEDURE FourN(Data: Vector; NN: IVector; isign: INTEGER); 
   (*
     Replaces DATA by its NDIM-dimensional discrete Fourier
     transform, if isign is input as 1.  NN[0, NDIM-1] is an integer array
     containing the lengths of each dimension (number of complex values),
     which MUST all be powers of 2. DATA is a real array of length twice 
     the product of these lengths, in which the data are stored as in a 
     multidimensional complex array: real and imaginary parts of each element 
     are in consecutive locations, and the rightmost index of the array 
     increases most rapidly as one proceeds along DATA. For a two-dimensional 
     array, this is equivalent to storing the array by rows.
     If isign is input as -1, DATA is replaced by its inverse
     transform times the product of the lengths of
     all dimensions.
   *)

END FourNM.