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57 lines
1.5 KiB
Fortran
57 lines
1.5 KiB
Fortran
*DECK ZSQRT
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SUBROUTINE ZSQRT (AR, AI, BR, BI)
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C***BEGIN PROLOGUE ZSQRT
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C***SUBSIDIARY
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C***PURPOSE Subsidiary to ZBESH, ZBESI, ZBESJ, ZBESK, ZBESY, ZAIRY and
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C ZBIRY
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C***LIBRARY SLATEC
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C***TYPE ALL (ZSQRT-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 DOUBLE PRECISION COMPLEX SQUARE ROOT, B=CSQRT(A)
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C
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C***SEE ALSO ZAIRY, ZBESH, ZBESI, ZBESJ, ZBESK, ZBESY, ZBIRY
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C***ROUTINES CALLED ZABS
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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***END PROLOGUE ZSQRT
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DOUBLE PRECISION AR, AI, BR, BI, ZM, DTHETA, DPI, DRT
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DOUBLE PRECISION ZABS
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EXTERNAL ZABS
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DATA DRT , DPI / 7.071067811865475244008443621D-1,
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1 3.141592653589793238462643383D+0/
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C***FIRST EXECUTABLE STATEMENT ZSQRT
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ZM = ZABS(AR,AI)
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ZM = SQRT(ZM)
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IF (AR.EQ.0.0D+0) GO TO 10
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IF (AI.EQ.0.0D+0) GO TO 20
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DTHETA = DATAN(AI/AR)
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IF (DTHETA.LE.0.0D+0) GO TO 40
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IF (AR.LT.0.0D+0) DTHETA = DTHETA - DPI
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GO TO 50
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10 IF (AI.GT.0.0D+0) GO TO 60
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IF (AI.LT.0.0D+0) GO TO 70
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BR = 0.0D+0
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BI = 0.0D+0
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RETURN
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20 IF (AR.GT.0.0D+0) GO TO 30
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BR = 0.0D+0
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BI = SQRT(ABS(AR))
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RETURN
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30 BR = SQRT(AR)
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BI = 0.0D+0
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RETURN
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40 IF (AR.LT.0.0D+0) DTHETA = DTHETA + DPI
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50 DTHETA = DTHETA*0.5D+0
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BR = ZM*COS(DTHETA)
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BI = ZM*SIN(DTHETA)
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RETURN
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60 BR = ZM*DRT
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BI = ZM*DRT
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RETURN
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70 BR = ZM*DRT
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BI = -ZM*DRT
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RETURN
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END
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