rffti1.f
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