
ACTION:
 From a rotation matrix, determine the corresponding axial vector (double
precision).

CALL:
CALL sla_DM2AV (RMAT, AXVEC)
GIVEN:
RMAT  D(3,3)  rotation matrix 

RETURNED:
AXVEC  D(3)  axial vector (radians) 


NOTES:


(1)
 A rotation matrix describes a rotation about some arbitrary axis, called the Euler
axis. The axial vector returned by this routine has the same direction as the Euler axis,
and its magnitude is the amount of rotation in radians.

(2)
 The magnitude and direction of the axial vector can be separated by means of the
routine sla_DVN.

(3)
 The reference frame rotates clockwise as seen looking along the axial vector from the
origin.

(4)
 If RMAT is null, so is the result.