# cffti1.f

          SUBROUTINE CFFTI1 (N, WA, IFAC)
    C***BEGIN PROLOGUE  CFFTI1
    C***PURPOSE  Initialize a real and an integer work array for CFFTF1 and
    C            CFFTB1.
    C***LIBRARY   SLATEC (FFTPACK)
    C***CATEGORY  J1A2
    C***TYPE      COMPLEX (RFFTI1-S, CFFTI1-C)
    C***KEYWORDS  FFTPACK, FOURIER TRANSFORM
    C***AUTHOR  Swarztrauber, P. N., (NCAR)
    C***DESCRIPTION
    C
    C  Subroutine CFFTI1 initializes the work arrays WA and IFAC which are
    C  used in both CFFTF1 and CFFTB1.  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 Parameter
    C
    C  N       the length of the sequence to be transformed
    C
    C  Output Parameters
    C
    C  WA      a real work array which must be dimensioned at least 2*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 CFFTF1 and CFFTB1
    C          as long as N remains unchanged.  Different WA and IFAC arrays
    C          are required for different values of N.  The contents of
    C          WA and IFAC must not be changed between calls of CFFTF1 or
    C          CFFTB1.
    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 function ATAN instead of a DATA
    C               statement.
    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  CFFTI1