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62 lines
1.9 KiB
Fortran
62 lines
1.9 KiB
Fortran
*DECK ZS1S2
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SUBROUTINE ZS1S2 (ZRR, ZRI, S1R, S1I, S2R, S2I, NZ, ASCLE, ALIM,
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+ IUF)
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C***BEGIN PROLOGUE ZS1S2
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C***SUBSIDIARY
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C***PURPOSE Subsidiary to ZAIRY and ZBESK
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C***LIBRARY SLATEC
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C***TYPE ALL (CS1S2-A, ZS1S2-A)
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C***AUTHOR Amos, D. E., (SNL)
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C***DESCRIPTION
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C
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C ZS1S2 TESTS FOR A POSSIBLE UNDERFLOW RESULTING FROM THE
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C ADDITION OF THE I AND K FUNCTIONS IN THE ANALYTIC CON-
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C TINUATION FORMULA WHERE S1=K FUNCTION AND S2=I FUNCTION.
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C ON KODE=1 THE I AND K FUNCTIONS ARE DIFFERENT ORDERS OF
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C MAGNITUDE, BUT FOR KODE=2 THEY CAN BE OF THE SAME ORDER
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C OF MAGNITUDE AND THE MAXIMUM MUST BE AT LEAST ONE
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C PRECISION ABOVE THE UNDERFLOW LIMIT.
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C
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C***SEE ALSO ZAIRY, ZBESK
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C***ROUTINES CALLED ZABS, ZEXP, ZLOG
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C***REVISION HISTORY (YYMMDD)
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C 830501 DATE WRITTEN
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C 910415 Prologue converted to Version 4.0 format. (BAB)
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C 930122 Added ZEXP and ZLOG to EXTERNAL statement. (RWC)
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C***END PROLOGUE ZS1S2
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C COMPLEX CZERO,C1,S1,S1D,S2,ZR
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DOUBLE PRECISION AA, ALIM, ALN, ASCLE, AS1, AS2, C1I, C1R, S1DI,
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* S1DR, S1I, S1R, S2I, S2R, ZEROI, ZEROR, ZRI, ZRR, ZABS
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INTEGER IUF, IDUM, NZ
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EXTERNAL ZABS, ZEXP, ZLOG
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DATA ZEROR,ZEROI / 0.0D0 , 0.0D0 /
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C***FIRST EXECUTABLE STATEMENT ZS1S2
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NZ = 0
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AS1 = ZABS(S1R,S1I)
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AS2 = ZABS(S2R,S2I)
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IF (S1R.EQ.0.0D0 .AND. S1I.EQ.0.0D0) GO TO 10
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IF (AS1.EQ.0.0D0) GO TO 10
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ALN = -ZRR - ZRR + LOG(AS1)
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S1DR = S1R
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S1DI = S1I
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S1R = ZEROR
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S1I = ZEROI
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AS1 = ZEROR
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IF (ALN.LT.(-ALIM)) GO TO 10
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CALL ZLOG(S1DR, S1DI, C1R, C1I, IDUM)
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C1R = C1R - ZRR - ZRR
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C1I = C1I - ZRI - ZRI
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CALL ZEXP(C1R, C1I, S1R, S1I)
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AS1 = ZABS(S1R,S1I)
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IUF = IUF + 1
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10 CONTINUE
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AA = MAX(AS1,AS2)
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IF (AA.GT.ASCLE) RETURN
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S1R = ZEROR
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S1I = ZEROI
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S2R = ZEROR
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S2I = ZEROI
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NZ = 1
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IUF = 0
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RETURN
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END
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