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