From d54fe7c1f704a63824c5bfa0ece65245572e9b27 Mon Sep 17 00:00:00 2001 From: Joseph Hunkeler Date: Wed, 4 Mar 2015 21:21:30 -0500 Subject: Initial commit --- src/slalib/dm2av.f | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 59 insertions(+) create mode 100644 src/slalib/dm2av.f (limited to 'src/slalib/dm2av.f') diff --git a/src/slalib/dm2av.f b/src/slalib/dm2av.f new file mode 100644 index 0000000..3f684fb --- /dev/null +++ b/src/slalib/dm2av.f @@ -0,0 +1,59 @@ + SUBROUTINE sla_DM2AV (RMAT, AXVEC) +*+ +* - - - - - - +* D M 2 A V +* - - - - - - +* +* 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 +* sla_DVN.) +* +* 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 +*- + + IMPLICIT NONE + + DOUBLE PRECISION RMAT(3,3),AXVEC(3) + + DOUBLE PRECISION X,Y,Z,S2,C2,PHI,F + + + + X = RMAT(2,3)-RMAT(3,2) + Y = RMAT(3,1)-RMAT(1,3) + Z = RMAT(1,2)-RMAT(2,1) + S2 = SQRT(X*X+Y*Y+Z*Z) + IF (S2.NE.0D0) THEN + C2 = (RMAT(1,1)+RMAT(2,2)+RMAT(3,3)-1D0) + PHI = ATAN2(S2/2D0,C2/2D0) + F = PHI/S2 + AXVEC(1) = X*F + AXVEC(2) = Y*F + AXVEC(3) = Z*F + ELSE + AXVEC(1) = 0D0 + AXVEC(2) = 0D0 + AXVEC(3) = 0D0 + END IF + + END -- cgit