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89 lines
2.5 KiB
Fortran
89 lines
2.5 KiB
Fortran
*DECK EZFFT1
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SUBROUTINE EZFFT1 (N, WA, IFAC)
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C***BEGIN PROLOGUE EZFFT1
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C***SUBSIDIARY
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C***PURPOSE EZFFTI calls EZFFT1 with appropriate work array
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C partitioning.
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C***LIBRARY SLATEC (FFTPACK)
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C***TYPE SINGLE PRECISION (EZFFT1-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 references to intrinsic function FLOAT
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C to REAL, and
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C (c) changing definition of variable TPI by using
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C FORTRAN intrinsic function ATAN 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 890531 Changed all specific intrinsics to generic. (WRB)
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C 890531 REVISION DATE from Version 3.2
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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 EZFFT1
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DIMENSION WA(*), IFAC(*), NTRYH(4)
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SAVE NTRYH
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DATA NTRYH(1),NTRYH(2),NTRYH(3),NTRYH(4)/4,2,3,5/
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C***FIRST EXECUTABLE STATEMENT EZFFT1
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TPI = 8.*ATAN(1.)
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NL = N
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NF = 0
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J = 0
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101 J = J+1
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IF (J-4) 102,102,103
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102 NTRY = NTRYH(J)
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GO TO 104
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103 NTRY = NTRY+2
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104 NQ = NL/NTRY
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NR = NL-NTRY*NQ
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IF (NR) 101,105,101
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105 NF = NF+1
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IFAC(NF+2) = NTRY
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NL = NQ
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IF (NTRY .NE. 2) GO TO 107
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IF (NF .EQ. 1) GO TO 107
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DO 106 I=2,NF
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IB = NF-I+2
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IFAC(IB+2) = IFAC(IB+1)
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106 CONTINUE
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IFAC(3) = 2
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107 IF (NL .NE. 1) GO TO 104
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IFAC(1) = N
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IFAC(2) = NF
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ARGH = TPI/N
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IS = 0
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NFM1 = NF-1
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L1 = 1
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IF (NFM1 .EQ. 0) RETURN
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DO 111 K1=1,NFM1
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IP = IFAC(K1+2)
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L2 = L1*IP
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IDO = N/L2
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IPM = IP-1
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ARG1 = L1*ARGH
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CH1 = 1.
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SH1 = 0.
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DCH1 = COS(ARG1)
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DSH1 = SIN(ARG1)
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DO 110 J=1,IPM
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CH1H = DCH1*CH1-DSH1*SH1
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SH1 = DCH1*SH1+DSH1*CH1
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CH1 = CH1H
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I = IS+2
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WA(I-1) = CH1
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WA(I) = SH1
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IF (IDO .LT. 5) GO TO 109
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DO 108 II=5,IDO,2
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I = I+2
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WA(I-1) = CH1*WA(I-3)-SH1*WA(I-2)
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WA(I) = CH1*WA(I-2)+SH1*WA(I-3)
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108 CONTINUE
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109 IS = IS+IDO
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110 CONTINUE
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L1 = L2
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111 CONTINUE
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RETURN
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END
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