pycsrt.f

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C*********************************************************************
 
C...PYCSRT
C...Auxiliary to PYCMQR
C
C     (YR,YI) = COMPLEX DSQRT(XR,XI)
C     BRANCH CHOSEN SO THAT YR .GE. 0.0 AND SIGN(YI) .EQ. SIGN(XI)
C
 
      SUBROUTINE pycsrt(XR,XI,YR,YI)
 
      DOUBLE PRECISION xr,xi,yr,yi
      DOUBLE PRECISION s,tr,ti,pythag
 
      tr = xr
      ti = xi
      s = dsqrt(0.5d0*(pythag(tr,ti) + dabs(tr)))
      IF (tr .GE. 0.0d0) yr = s
      IF (ti .LT. 0.0d0) s = -s
      IF (tr .LE. 0.0d0) yi = s
      IF (tr .LT. 0.0d0) yr = 0.5d0*(ti/yi)
      IF (tr .GT. 0.0d0) yi = 0.5d0*(ti/yr)
      RETURN
      END