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SUBROUTINE sla_AV2M (AXVEC, RMAT)
*+
* - - - - -
* A V 2 M
* - - - - -
*
* Form the rotation matrix corresponding to a given axial vector.
*
* (single 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 supplied to this routine has the same direction as the
* Euler axis, and its magnitude is the Euler angle in radians.
*
* Given:
* AXVEC r(3) axial vector (radians)
*
* Returned:
* RMAT r(3,3) rotation matrix
*
* If AXVEC is null, the unit matrix is returned.
*
* The reference frame rotates clockwise as seen looking along
* the axial vector from the origin.
*
* P.T.Wallace Starlink June 1989
*
* Copyright (C) 1995 Rutherford Appleton Laboratory
*-
IMPLICIT NONE
REAL AXVEC(3),RMAT(3,3)
REAL X,Y,Z,PHI,S,C,W
* Euler angle - magnitude of axial vector - and functions
X = AXVEC(1)
Y = AXVEC(2)
Z = AXVEC(3)
PHI = SQRT(X*X+Y*Y+Z*Z)
S = SIN(PHI)
C = COS(PHI)
W = 1.0-C
* Euler axis - direction of axial vector (perhaps null)
IF (PHI.NE.0.0) THEN
X = X/PHI
Y = Y/PHI
Z = Z/PHI
END IF
* Compute the rotation matrix
RMAT(1,1) = X*X*W+C
RMAT(1,2) = X*Y*W+Z*S
RMAT(1,3) = X*Z*W-Y*S
RMAT(2,1) = X*Y*W-Z*S
RMAT(2,2) = Y*Y*W+C
RMAT(2,3) = Y*Z*W+X*S
RMAT(3,1) = X*Z*W+Y*S
RMAT(3,2) = Y*Z*W-X*S
RMAT(3,3) = Z*Z*W+C
END
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