 
C
C
C                    * * * * * * * * * * * * * * * *
C                    *                             *
C                    * SUBROUTINE VSRFTI(N,WSAVE)  *
C                    *                             *
C                    * * * * * * * * * * * * * * * *
C
C
C                           * * * * * * * *
C                           *   PURPOSE   *
C                           * * * * * * * *
C
C
C     A SUBROUTINE THAT COMPUTES INTERMEDIATE VALUES REQUIRED FOR THE
C     CALCULATION OF A REAL PERIODIC FAST FOURIER TRANSFORM.
C
C
C     NOTE:  SUBROUTINE VSRFTI MUST BE CALLED BEFORE EITHER SUBROUTINES
C     VSRFTF OR VSRFTB IS CALLED, BUT IT NEED BE CALLED ONLY ONCE FOR
C     A GIVEN VALUE OF N.
C
C
C
C                    * * * * * * * * * * * * * * *
C                    *   PARAMETER DESCRIPTION   *
C                    * * * * * * * * * * * * * * *
C
C
C     INPUT PARAMETER
C
C     N      THE LENGTH OF THE TRANSFORM TO BE COMPUTED.
C
C
C     OUTPUT PARAMETER
C
C     WSAVE  A REAL ONE-DIMENSIONAL ARRAY OF LENGTH N+15 THAT CONTAINS
C            INTERMEDIATE VALUES REQUIRED IN THE CALCULATION OF A REAL
C            PERIODIC FAST FOURIER TRANSFORM BY SUBROUTINE VRFFTF OR
C            VRFFTF.
C
C     NOTE:  THE QUANTITIES IN THE ARRAY WSAVE MUST NOT BE DESTROYED
C            BETWEEN CALLS TO SUBROUTINES VSRFTF OR VSRFTB.
C
C
C
C              * * * * * * * * * * * * * * * * * * * * *
C              *                                       *
C              *         PROGRAM SPECIFICATIONS        *
C              *                                       *
C              * * * * * * * * * * * * * * * * * * * * *
C
C
C
C     DIMENSION OF    F(L,M,N), FT(L*M*N), C1(M), C2(M), C3(M), C4(M),
C     ARGUMENTS       WSAVE(N+15)
C
C     LATEST          AUGUST 1, 1985
C     REVISION
C
C     SUBPROGRAMS     VSRFTI, VSCOSI, VSCSQI, VSRFTF, VSRFTB, VSCOSF,
C     REQUIRED        VSCOSB, VSCOSQ, VSSINF, VSSINB, VSSINQ, PIMACH,
C                     VRFFTPK (PACKAGE)
C
C     SPECIAL         NONE
C     CONDITIONS
C
C     COMMON          NONE
C     BLOCKS
C
C     I/O             NONE
C
C     PRECISION       SINGLE
C
C     SPECIALIST      ROLAND SWEET
C
C     LANGUAGE        FORTRAN
C
C     HISTORY         WRITTEN BY LINDA LINDGREN AND ROLAND SWEET AT THE
C                     NATIONAL BUREAU OF STANDARDS (BOULDER).
C
C     ALGORITHM       SEE "FAST FOURIER TRANSFORMS ON A STAGGERED GRID"
C                     BY ROLAND A. SWEET (TO APPEAR)
C
C     PORTABILITY     AMERICAN NATIONAL STANDARDS INSTITUTE FORTRAN 77.
C                     THE ONLY MACHINE DEPENDENT CONSTANT IS LOCATED IN
C                     THE FUNCTION PIMACH.
C
C     REQUIRED        COS,SIN
C     RESIDENT
C     ROUTINES
C
 
 
