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85 lines
2.9 KiB
Fortran
85 lines
2.9 KiB
Fortran
*DECK RADB3
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SUBROUTINE RADB3 (IDO, L1, CC, CH, WA1, WA2)
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C***BEGIN PROLOGUE RADB3
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C***SUBSIDIARY
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C***PURPOSE Calculate the fast Fourier transform of subvectors of
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C length three.
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C***LIBRARY SLATEC (FFTPACK)
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C***TYPE SINGLE PRECISION (RADB3-S)
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C***AUTHOR Swarztrauber, P. N., (NCAR)
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C***ROUTINES CALLED (NONE)
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C***REVISION HISTORY (YYMMDD)
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C 790601 DATE WRITTEN
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C 830401 Modified to use SLATEC library source file format.
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C 860115 Modified by Ron Boisvert to adhere to Fortran 77 by
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C (a) changing dummy array size declarations (1) to (*),
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C (b) changing definition of variable TAUI by using
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C FORTRAN intrinsic function SQRT instead of a DATA
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C statement.
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C 881128 Modified by Dick Valent to meet prologue standards.
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C 890831 Modified array declarations. (WRB)
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 900402 Added TYPE section. (WRB)
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C***END PROLOGUE RADB3
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DIMENSION CC(IDO,3,*), CH(IDO,L1,3), WA1(*), WA2(*)
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C***FIRST EXECUTABLE STATEMENT RADB3
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TAUR = -.5
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TAUI = .5*SQRT(3.)
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DO 101 K=1,L1
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TR2 = CC(IDO,2,K)+CC(IDO,2,K)
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CR2 = CC(1,1,K)+TAUR*TR2
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CH(1,K,1) = CC(1,1,K)+TR2
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CI3 = TAUI*(CC(1,3,K)+CC(1,3,K))
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CH(1,K,2) = CR2-CI3
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CH(1,K,3) = CR2+CI3
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101 CONTINUE
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IF (IDO .EQ. 1) RETURN
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IDP2 = IDO+2
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IF((IDO-1)/2.LT.L1) GO TO 104
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DO 103 K=1,L1
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CDIR$ IVDEP
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DO 102 I=3,IDO,2
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IC = IDP2-I
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TR2 = CC(I-1,3,K)+CC(IC-1,2,K)
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CR2 = CC(I-1,1,K)+TAUR*TR2
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CH(I-1,K,1) = CC(I-1,1,K)+TR2
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TI2 = CC(I,3,K)-CC(IC,2,K)
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CI2 = CC(I,1,K)+TAUR*TI2
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CH(I,K,1) = CC(I,1,K)+TI2
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CR3 = TAUI*(CC(I-1,3,K)-CC(IC-1,2,K))
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CI3 = TAUI*(CC(I,3,K)+CC(IC,2,K))
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DR2 = CR2-CI3
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DR3 = CR2+CI3
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DI2 = CI2+CR3
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DI3 = CI2-CR3
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CH(I-1,K,2) = WA1(I-2)*DR2-WA1(I-1)*DI2
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CH(I,K,2) = WA1(I-2)*DI2+WA1(I-1)*DR2
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CH(I-1,K,3) = WA2(I-2)*DR3-WA2(I-1)*DI3
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CH(I,K,3) = WA2(I-2)*DI3+WA2(I-1)*DR3
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102 CONTINUE
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103 CONTINUE
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RETURN
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104 DO 106 I=3,IDO,2
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IC = IDP2-I
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CDIR$ IVDEP
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DO 105 K=1,L1
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TR2 = CC(I-1,3,K)+CC(IC-1,2,K)
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CR2 = CC(I-1,1,K)+TAUR*TR2
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CH(I-1,K,1) = CC(I-1,1,K)+TR2
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TI2 = CC(I,3,K)-CC(IC,2,K)
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CI2 = CC(I,1,K)+TAUR*TI2
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CH(I,K,1) = CC(I,1,K)+TI2
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CR3 = TAUI*(CC(I-1,3,K)-CC(IC-1,2,K))
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CI3 = TAUI*(CC(I,3,K)+CC(IC,2,K))
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DR2 = CR2-CI3
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DR3 = CR2+CI3
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DI2 = CI2+CR3
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DI3 = CI2-CR3
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CH(I-1,K,2) = WA1(I-2)*DR2-WA1(I-1)*DI2
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CH(I,K,2) = WA1(I-2)*DI2+WA1(I-1)*DR2
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CH(I-1,K,3) = WA2(I-2)*DR3-WA2(I-1)*DI3
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CH(I,K,3) = WA2(I-2)*DI3+WA2(I-1)*DR3
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105 CONTINUE
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106 CONTINUE
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RETURN
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END
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