*DECK SINTI SUBROUTINE SINTI (N, WSAVE) C***BEGIN PROLOGUE SINTI C***PURPOSE Initialize a work array for SINT. C***LIBRARY SLATEC (FFTPACK) C***CATEGORY J1A3 C***TYPE SINGLE PRECISION (SINTI-S) C***KEYWORDS FFTPACK, FOURIER TRANSFORM C***AUTHOR Swarztrauber, P. N., (NCAR) C***DESCRIPTION C C Subroutine SINTI initializes the array WSAVE which is used in C subroutine SINT. The prime factorization of N together with C a tabulation of the trigonometric functions are computed and C stored in WSAVE. C C Input Parameter C C N the length of the sequence to be transformed. The method C is most efficient when N+1 is a product of small primes. C C Output Parameter C C WSAVE a work array with at least INT(3.5*N+16) locations. C Different WSAVE arrays are required for different values C of N. The contents of WSAVE must not be changed between C calls of SINT. 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 RFFTI 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 PI 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 890531 REVISION DATE from Version 3.2 C 891214 Prologue converted to Version 4.0 format. (BAB) C 920501 Reformatted the REFERENCES section. (WRB) C***END PROLOGUE SINTI DIMENSION WSAVE(*) C***FIRST EXECUTABLE STATEMENT SINTI IF (N .LE. 1) RETURN PI = 4.*ATAN(1.) NP1 = N+1 NS2 = N/2 DT = PI/NP1 KS = N+2 KF = KS+NS2-1 FK = 0. DO 101 K=KS,KF FK = FK+1. WSAVE(K) = 2.*SIN(FK*DT) 101 CONTINUE CALL RFFTI (NP1,WSAVE(KF+1)) RETURN END