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- *DECK CS1S2
- SUBROUTINE CS1S2 (ZR, S1, S2, NZ, ASCLE, ALIM, IUF)
- C***BEGIN PROLOGUE CS1S2
- C***SUBSIDIARY
- C***PURPOSE Subsidiary to CAIRY and CBESK
- C***LIBRARY SLATEC
- C***TYPE ALL (CS1S2-A, ZS1S2-A)
- C***AUTHOR Amos, D. E., (SNL)
- C***DESCRIPTION
- C
- C CS1S2 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***SEE ALSO CAIRY, CBESK
- C***ROUTINES CALLED (NONE)
- C***REVISION HISTORY (YYMMDD)
- C 830501 DATE WRITTEN
- C 910415 Prologue converted to Version 4.0 format. (BAB)
- C***END PROLOGUE CS1S2
- COMPLEX CZERO, C1, S1, S1D, S2, ZR
- REAL AA, ALIM, ALN, ASCLE, AS1, AS2, XX
- INTEGER IUF, NZ
- DATA CZERO / (0.0E0,0.0E0) /
- C***FIRST EXECUTABLE STATEMENT CS1S2
- NZ = 0
- AS1 = ABS(S1)
- AS2 = ABS(S2)
- AA = REAL(S1)
- ALN = AIMAG(S1)
- IF (AA.EQ.0.0E0 .AND. ALN.EQ.0.0E0) GO TO 10
- IF (AS1.EQ.0.0E0) GO TO 10
- XX = REAL(ZR)
- ALN = -XX - XX + ALOG(AS1)
- S1D = S1
- S1 = CZERO
- AS1 = 0.0E0
- IF (ALN.LT.(-ALIM)) GO TO 10
- C1 = CLOG(S1D) - ZR - ZR
- S1 = CEXP(C1)
- AS1 = ABS(S1)
- IUF = IUF + 1
- 10 CONTINUE
- AA = MAX(AS1,AS2)
- IF (AA.GT.ASCLE) RETURN
- S1 = CZERO
- S2 = CZERO
- NZ = 1
- IUF = 0
- RETURN
- END
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