SLATEC Routines --- RFFTI1 ---

*DECK RFFTI1
      SUBROUTINE RFFTI1 (N, WA, IFAC)
C***BEGIN PROLOGUE  RFFTI1
C***PURPOSE  Initialize a real and an integer work array for RFFTF1 and
C            RFFTB1.
C***LIBRARY   SLATEC (FFTPACK)
C***CATEGORY  J1A1
C***TYPE      SINGLE PRECISION (RFFTI1-S, CFFTI1-C)
C***KEYWORDS  FFTPACK, FOURIER TRANSFORM
C***AUTHOR  Swarztrauber, P. N., (NCAR)
C***DESCRIPTION
C
C   Subroutine RFFTI1 initializes the work arrays WA and IFAC which are
C   used in both RFFTF1 and RFFTB1.  The prime factorization of N and a
C   tabulation of the trigonometric functions are computed and stored in
C   IFAC and WA, respectively.
C
C   Input Argument
C
C   N       the length of the sequence to be transformed.
C
C   Output Arguments
C
C   WA      a real work array which must be dimensioned at least N.
C
C   IFAC    an integer work array which must be dimensioned at least 15.
C
C   The same work arrays can be used for both RFFTF1 and RFFTB1 as long
C   as N remains unchanged.  Different WA and IFAC arrays are required
C   for different values of N.  The contents of WA and IFAC must not be
C   changed between calls of RFFTF1 or RFFTB1.
C
C***REFERENCES  P. N. Swarztrauber, Vectorizing the FFTs, in Parallel
C                 Computations (G. Rodrigue, ed.), Academic Press,
C                 1982, pp. 51-83.
C***ROUTINES CALLED  (NONE)
C***REVISION HISTORY  (YYMMDD)
C   790601  DATE WRITTEN
C   830401  Modified to use SLATEC library source file format.
C   860115  Modified by Ron Boisvert to adhere to Fortran 77 by
C           (a) changing dummy array size declarations (1) to (*),
C           (b) changing references to intrinsic function FLOAT
C               to REAL, and
C           (c) changing definition of variable TPI by using
C               FORTRAN intrinsic functions instead of DATA
C               statements.
C   881128  Modified by Dick Valent to meet prologue standards.
C   890531  Changed all specific intrinsics to generic.  (WRB)
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   900131  Routine changed from subsidiary to user-callable.  (WRB)
C   920501  Reformatted the REFERENCES section.  (WRB)
C***END PROLOGUE  RFFTI1