COSQI(3)

SYNOPSIS
SUBROUTINE COSQI (N, WSAVE)

NAME
cosqi - Initialize a work array for COSQF and COSQB.

LIBRARY
SLATEC (FFTPACK)

CATEGORY
J1A3

TYPE
SINGLE PRECISION (COSQI-S)

KEYWORDS
COSINE FOURIER TRANSFORM, FFTPACK

AUTHOR
Swarztrauber, P. N., (NCAR)

DESCRIPTION
Subroutine COSQI initializes the work array WSAVE which is used in both COSQF1 and COSQB1. The prime factorization of N together with a tabulation of the trigonometric functions are computed and stored in WSAVE. Input Parameter N the length of the array to be transformed. The method is most efficient when N is a product of small primes. Output Parameter WSAVE a work array which must be dimensioned at least 3*N+15. The same work array can be used for both COSQF1 and COSQB1 as long as N remains unchanged. Different WSAVE arrays are required for different values of N. The contents of WSAVE must not be changed between calls of COSQF1 or COSQB1.

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

ROUTINES CALLED
RFFTI

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 PIH by using FORTRAN intrinsic function ATAN instead of a DATA statement.
881128 Modified by Dick Valent to meet prologue standards.
890531 Changed all specific intrinsics to generic. (WRB)
890531 REVISION DATE from Version 3.2
891214 Prologue converted to Version 4.0 format. (BAB)
920501 Reformatted the REFERENCES section. (WRB)