*DECK COSQB1 SUBROUTINE COSQB1 (N, X, W, XH) C***BEGIN PROLOGUE COSQB1 C***SUBSIDIARY C***PURPOSE Compute the unnormalized inverse of COSQF1. C***LIBRARY SLATEC (FFTPACK) C***CATEGORY J1A3 C***TYPE SINGLE PRECISION (COSQB1-S) C***KEYWORDS FFTPACK, FOURIER TRANSFORM C***AUTHOR Swarztrauber, P. N., (NCAR) C***DESCRIPTION C C Subroutine COSQB1 computes the fast Fourier transform of quarter C wave data. That is, COSQB1 computes a sequence from its C representation in terms of a cosine series with odd wave numbers. C The transform is defined below at output parameter X. 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 RFFTB 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 changing dummy array size declarations (1) to (*). C 881128 Modified by Dick Valent to meet prologue standards. C 891214 Prologue converted to Version 4.0 format. (BAB) C 920501 Reformatted the REFERENCES section. (WRB) C***END PROLOGUE COSQB1 DIMENSION X(*), W(*), XH(*) C***FIRST EXECUTABLE STATEMENT COSQB1 NS2 = (N+1)/2 NP2 = N+2 DO 101 I=3,N,2 XIM1 = X(I-1)+X(I) X(I) = X(I)-X(I-1) X(I-1) = XIM1 101 CONTINUE X(1) = X(1)+X(1) MODN = MOD(N,2) IF (MODN .EQ. 0) X(N) = X(N)+X(N) CALL RFFTB (N,X,XH) DO 102 K=2,NS2 KC = NP2-K XH(K) = W(K-1)*X(KC)+W(KC-1)*X(K) XH(KC) = W(K-1)*X(K)-W(KC-1)*X(KC) 102 CONTINUE IF (MODN .EQ. 0) X(NS2+1) = W(NS2)*(X(NS2+1)+X(NS2+1)) DO 103 K=2,NS2 KC = NP2-K X(K) = XH(K)+XH(KC) X(KC) = XH(K)-XH(KC) 103 CONTINUE X(1) = X(1)+X(1) RETURN END