DEFINITION MODULE Four1M;

   (* EXPORT QUALIFIED Four1; *)

   FROM NRVect IMPORT Vector;

   PROCEDURE Four1(DATA:  Vector; nn, isign: INTEGER); 
   (*
     Replaces DATA by its discrete Fourier transform, if isign
     is input as 1; or replaces DATA by nn times its inverse
     discrete Fourier transform, if isign is input as -1.  DATA is
     a complex array of length nn, input as a real array
     DATA[0, 2*nn-1]. nn MUST be an integer power of 2 (this is not 
     checked for!).
   *)

END Four1M.