RFFTI1(3)

SYNOPSIS
SUBROUTINE RFFTI1 (N, WA, IFAC)

NAME
rffti1 - Initialize a real and an integer work array for RFFTF1 and RFFTB1.

LIBRARY
SLATEC (FFTPACK)

CATEGORY
J1A1

TYPE
SINGLE PRECISION (RFFTI1-S, CFFTI1-C)

KEYWORDS
FFTPACK, FOURIER TRANSFORM

AUTHOR
Swarztrauber, P. N., (NCAR)

DESCRIPTION
Subroutine RFFTI1 initializes the work arrays WA and IFAC which are used in both RFFTF1 and RFFTB1. The prime factorization of N and a tabulation of the trigonometric functions are computed and stored in IFAC and WA, respectively. Input Argument N the length of the sequence to be transformed. Output Arguments WA a real work array which must be dimensioned at least N. IFAC an integer work array which must be dimensioned at least 15. The same work arrays can be used for both RFFTF1 and RFFTB1 as long as N remains unchanged. Different WA and IFAC arrays are required for different values of N. The contents of WA and IFAC must not be changed between calls of RFFTF1 or RFFTB1.

REFERENCES
P. N. Swarztrauber, Vectorizing the FFTs, in Parallel Computations (G. Rodrigue, ed.), Academic Press, 1982, pp. 51-83.

ROUTINES CALLED
(NONE)

REVISION HISTORY (YYMMDD)
790601 DATE WRITTEN
830401 Modified to use SLATEC library source file format.
860115 Modified by Ron Boisvert to adhere to Fortran 77 by (a) changing dummy array size declarations (1) to (*), (b) changing references to intrinsic function FLOAT to REAL, and (c) changing definition of variable TPI by using FORTRAN intrinsic functions instead of DATA statements.
881128 Modified by Dick Valent to meet prologue standards.
890531 Changed all specific intrinsics to generic. (WRB)
891214 Prologue converted to Version 4.0 format. (BAB)
900131 Routine changed from subsidiary to user-callable. (WRB)
920501 Reformatted the REFERENCES section. (WRB)