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- *DECK CSROOT
- SUBROUTINE CSROOT (XR, XI, YR, YI)
- C***BEGIN PROLOGUE CSROOT
- C***SUBSIDIARY
- C***PURPOSE Compute the complex square root of a complex number.
- C***LIBRARY SLATEC
- C***TYPE SINGLE PRECISION (CSROOT-S)
- C***AUTHOR (UNKNOWN)
- C***DESCRIPTION
- C
- C (YR,YI) = complex sqrt(XR,XI)
- C
- C***SEE ALSO EISDOC
- C***ROUTINES CALLED PYTHAG
- C***REVISION HISTORY (YYMMDD)
- C 811101 DATE WRITTEN
- C 891214 Prologue converted to Version 4.0 format. (BAB)
- C 900402 Added TYPE section. (WRB)
- C***END PROLOGUE CSROOT
- REAL XR,XI,YR,YI,S,TR,TI,PYTHAG
- C
- C BRANCH CHOSEN SO THAT YR .GE. 0.0 AND SIGN(YI) .EQ. SIGN(XI)
- C***FIRST EXECUTABLE STATEMENT CSROOT
- TR = XR
- TI = XI
- S = SQRT(0.5E0*(PYTHAG(TR,TI) + ABS(TR)))
- IF (TR .GE. 0.0E0) YR = S
- IF (TI .LT. 0.0E0) S = -S
- IF (TR .LE. 0.0E0) YI = S
- IF (TR .LT. 0.0E0) YR = 0.5E0*(TI/YI)
- IF (TR .GT. 0.0E0) YI = 0.5E0*(TI/YR)
- RETURN
- END
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