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- *DECK ZSQRT
- SUBROUTINE ZSQRT (AR, AI, BR, BI)
- C***BEGIN PROLOGUE ZSQRT
- C***SUBSIDIARY
- C***PURPOSE Subsidiary to ZBESH, ZBESI, ZBESJ, ZBESK, ZBESY, ZAIRY and
- C ZBIRY
- C***LIBRARY SLATEC
- C***TYPE ALL (ZSQRT-A)
- C***AUTHOR Amos, D. E., (SNL)
- C***DESCRIPTION
- C
- C DOUBLE PRECISION COMPLEX SQUARE ROOT, B=CSQRT(A)
- C
- C***SEE ALSO ZAIRY, ZBESH, ZBESI, ZBESJ, ZBESK, ZBESY, ZBIRY
- C***ROUTINES CALLED ZABS
- C***REVISION HISTORY (YYMMDD)
- C 830501 DATE WRITTEN
- C 910415 Prologue converted to Version 4.0 format. (BAB)
- C***END PROLOGUE ZSQRT
- DOUBLE PRECISION AR, AI, BR, BI, ZM, DTHETA, DPI, DRT
- DOUBLE PRECISION ZABS
- EXTERNAL ZABS
- DATA DRT , DPI / 7.071067811865475244008443621D-1,
- 1 3.141592653589793238462643383D+0/
- C***FIRST EXECUTABLE STATEMENT ZSQRT
- ZM = ZABS(AR,AI)
- ZM = SQRT(ZM)
- IF (AR.EQ.0.0D+0) GO TO 10
- IF (AI.EQ.0.0D+0) GO TO 20
- DTHETA = DATAN(AI/AR)
- IF (DTHETA.LE.0.0D+0) GO TO 40
- IF (AR.LT.0.0D+0) DTHETA = DTHETA - DPI
- GO TO 50
- 10 IF (AI.GT.0.0D+0) GO TO 60
- IF (AI.LT.0.0D+0) GO TO 70
- BR = 0.0D+0
- BI = 0.0D+0
- RETURN
- 20 IF (AR.GT.0.0D+0) GO TO 30
- BR = 0.0D+0
- BI = SQRT(ABS(AR))
- RETURN
- 30 BR = SQRT(AR)
- BI = 0.0D+0
- RETURN
- 40 IF (AR.LT.0.0D+0) DTHETA = DTHETA + DPI
- 50 DTHETA = DTHETA*0.5D+0
- BR = ZM*COS(DTHETA)
- BI = ZM*SIN(DTHETA)
- RETURN
- 60 BR = ZM*DRT
- BI = ZM*DRT
- RETURN
- 70 BR = ZM*DRT
- BI = -ZM*DRT
- RETURN
- END
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