zsqrt.f 1.2 KB

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  1. SUBROUTINE ZSQRT(AR, AI, BR, BI)
  2. C***BEGIN PROLOGUE ZSQRT
  3. C***REFER TO ZBESH,ZBESI,ZBESJ,ZBESK,ZBESY,ZAIRY,ZBIRY
  4. C
  5. C DOUBLE PRECISION COMPLEX SQUARE ROOT, B=CSQRT(A)
  6. C
  7. C***ROUTINES CALLED ZABS
  8. C***END PROLOGUE ZSQRT
  9. DOUBLE PRECISION AR, AI, BR, BI, ZM, DTHETA, DPI, DRT
  10. DOUBLE PRECISION ZABS
  11. DATA DRT , DPI / 7.071067811865475244008443621D-1,
  12. 1 3.141592653589793238462643383D+0/
  13. ZM = ZABS(COMPLEX(AR,AI))
  14. ZM = DSQRT(ZM)
  15. IF (AR.EQ.0.0D+0) GO TO 10
  16. IF (AI.EQ.0.0D+0) GO TO 20
  17. DTHETA = DATAN(AI/AR)
  18. IF (DTHETA.LE.0.0D+0) GO TO 40
  19. IF (AR.LT.0.0D+0) DTHETA = DTHETA - DPI
  20. GO TO 50
  21. 10 IF (AI.GT.0.0D+0) GO TO 60
  22. IF (AI.LT.0.0D+0) GO TO 70
  23. BR = 0.0D+0
  24. BI = 0.0D+0
  25. RETURN
  26. 20 IF (AR.GT.0.0D+0) GO TO 30
  27. BR = 0.0D+0
  28. BI = DSQRT(DABS(AR))
  29. RETURN
  30. 30 BR = DSQRT(AR)
  31. BI = 0.0D+0
  32. RETURN
  33. 40 IF (AR.LT.0.0D+0) DTHETA = DTHETA + DPI
  34. 50 DTHETA = DTHETA*0.5D+0
  35. BR = ZM*DCOS(DTHETA)
  36. BI = ZM*DSIN(DTHETA)
  37. RETURN
  38. 60 BR = ZM*DRT
  39. BI = ZM*DRT
  40. RETURN
  41. 70 BR = ZM*DRT
  42. BI = -ZM*DRT
  43. RETURN
  44. END