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56 lines
1.9 KiB
Fortran
56 lines
1.9 KiB
Fortran
*DECK PASSB2
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SUBROUTINE PASSB2 (IDO, L1, CC, CH, WA1)
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C***BEGIN PROLOGUE PASSB2
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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 two.
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C***LIBRARY SLATEC (FFTPACK)
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C***TYPE SINGLE PRECISION (PASSB2-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 changing dummy array size declarations (1) to (*).
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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 PASSB2
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DIMENSION CC(IDO,2,*), CH(IDO,L1,2), WA1(*)
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C***FIRST EXECUTABLE STATEMENT PASSB2
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IF (IDO .GT. 2) GO TO 102
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DO 101 K=1,L1
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CH(1,K,1) = CC(1,1,K)+CC(1,2,K)
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CH(1,K,2) = CC(1,1,K)-CC(1,2,K)
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CH(2,K,1) = CC(2,1,K)+CC(2,2,K)
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CH(2,K,2) = CC(2,1,K)-CC(2,2,K)
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101 CONTINUE
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RETURN
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102 IF(IDO/2.LT.L1) GO TO 105
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DO 104 K=1,L1
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CDIR$ IVDEP
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DO 103 I=2,IDO,2
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CH(I-1,K,1) = CC(I-1,1,K)+CC(I-1,2,K)
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TR2 = CC(I-1,1,K)-CC(I-1,2,K)
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CH(I,K,1) = CC(I,1,K)+CC(I,2,K)
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TI2 = CC(I,1,K)-CC(I,2,K)
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CH(I,K,2) = WA1(I-1)*TI2+WA1(I)*TR2
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CH(I-1,K,2) = WA1(I-1)*TR2-WA1(I)*TI2
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103 CONTINUE
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104 CONTINUE
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RETURN
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105 DO 107 I=2,IDO,2
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CDIR$ IVDEP
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DO 106 K=1,L1
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CH(I-1,K,1) = CC(I-1,1,K)+CC(I-1,2,K)
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TR2 = CC(I-1,1,K)-CC(I-1,2,K)
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CH(I,K,1) = CC(I,1,K)+CC(I,2,K)
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TI2 = CC(I,1,K)-CC(I,2,K)
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CH(I,K,2) = WA1(I-1)*TI2+WA1(I)*TR2
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CH(I-1,K,2) = WA1(I-1)*TR2-WA1(I)*TI2
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106 CONTINUE
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107 CONTINUE
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RETURN
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END
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