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- SUBROUTINE ZS1S2(ZRR, ZRI, S1R, S1I, S2R, S2I, NZ, ASCLE, ALIM,
- * IUF)
- C***BEGIN PROLOGUE ZS1S2
- C***REFER TO ZBESK,ZAIRY
- C
- C ZS1S2 TESTS FOR A POSSIBLE UNDERFLOW RESULTING FROM THE
- C ADDITION OF THE I AND K FUNCTIONS IN THE ANALYTIC CON-
- C TINUATION FORMULA WHERE S1=K FUNCTION AND S2=I FUNCTION.
- C ON KODE=1 THE I AND K FUNCTIONS ARE DIFFERENT ORDERS OF
- C MAGNITUDE, BUT FOR KODE=2 THEY CAN BE OF THE SAME ORDER
- C OF MAGNITUDE AND THE MAXIMUM MUST BE AT LEAST ONE
- C PRECISION ABOVE THE UNDERFLOW LIMIT.
- C
- C***ROUTINES CALLED ZABS,ZEXP,ZLOG
- C***END PROLOGUE ZS1S2
- C COMPLEX CZERO,C1,S1,S1D,S2,ZR
- DOUBLE PRECISION AA, ALIM, ALN, ASCLE, AS1, AS2, C1I, C1R, S1DI,
- * S1DR, S1I, S1R, S2I, S2R, ZEROI, ZEROR, ZRI, ZRR, ZABS
- INTEGER IUF, IDUM, NZ
- DATA ZEROR,ZEROI / 0.0D0 , 0.0D0 /
- NZ = 0
- AS1 = ZABS(COMPLEX(S1R,S1I))
- AS2 = ZABS(COMPLEX(S2R,S2I))
- IF (S1R.EQ.0.0D0 .AND. S1I.EQ.0.0D0) GO TO 10
- IF (AS1.EQ.0.0D0) GO TO 10
- ALN = -ZRR - ZRR + DLOG(AS1)
- S1DR = S1R
- S1DI = S1I
- S1R = ZEROR
- S1I = ZEROI
- AS1 = ZEROR
- IF (ALN.LT.(-ALIM)) GO TO 10
- CALL ZLOG(S1DR, S1DI, C1R, C1I, IDUM)
- C1R = C1R - ZRR - ZRR
- C1I = C1I - ZRI - ZRI
- CALL ZEXP(C1R, C1I, S1R, S1I)
- AS1 = ZABS(COMPLEX(S1R,S1I))
- IUF = IUF + 1
- 10 CONTINUE
- AA = DMAX1(AS1,AS2)
- IF (AA.GT.ASCLE) RETURN
- S1R = ZEROR
- S1I = ZEROI
- S2R = ZEROR
- S2I = ZEROI
- NZ = 1
- IUF = 0
- RETURN
- END
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