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