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      SUBROUTINE slDMAV (RMAT, AXVEC)

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      D M A V
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  From a rotation matrix, determine the corresponding axial vector.
  (double precision)

  A rotation matrix describes a rotation about some arbitrary axis.
  The axis is called the Euler axis, and the angle through which the
  reference frame rotates is called the Euler angle.  The axial
  vector returned by this routine has the same direction as the
  Euler axis, and its magnitude is the Euler angle in radians.  (The
  magnitude and direction can be separated by means of the routine
  slDVN.)

  Given:
    RMAT   d(3,3)   rotation matrix

  Returned:
    AXVEC  d(3)     axial vector (radians)

  The reference frame rotates clockwise as seen looking along
  the axial vector from the origin.

  If RMAT is null, so is the result.

  P.T.Wallace   Starlink   24 December 1992

  Copyright (C) 1995 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

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