ksrot.f

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      SUBROUTINE ksrot(U,UDOT,THETA)
*
*       KS Orbit rotation.
*       -----------------
*       Authors: D.J. Urminsky & D.C. Heggie (2005).
*
      IMPLICIT REAL*8 (a-h,o-z)
      REAL*8 u(4),udot(4),uhat(4),v(4),vhat(4),uhat2(4),vhat2(4)
*
      us = sqrt(u(1)**2 + u(2)**2 + u(3)**2 + u(4)**2)
      udotr = 0.0
      DO 5 k = 1,4
          uhat(k) = u(k)/us
          udotr = udotr + udot(k)*uhat(k)
    5 CONTINUE
*
      vs = 0.0
      DO 10 k = 1,4
          v(k) = udot(k) - udotr*uhat(k)
          vs = vs + v(k)**2
   10 CONTINUE
      vs = sqrt(vs)
      DO 15 k = 1,4
          vhat(k) = v(k)/vs
   15 CONTINUE
*
*       Perform the rotation of physical angle THETA.
      DO 20 k = 1,4
          uhat2(k) = uhat(k)*cos(0.5d0*theta) + vhat(k)*sin(0.5d0*theta)
          vhat2(k) = vhat(k)*cos(0.5d0*theta) - uhat(k)*sin(0.5d0*theta)
          u(k) = us*uhat2(k)
          udot(k) = udotr*uhat2(k) + vs*vhat2(k)
   20 CONTINUE
*
      RETURN
      END