From fa080de7afc95aa1c19a6e6fc0e0708ced2eadc4 Mon Sep 17 00:00:00 2001
From: Joseph Hunkeler <jhunkeler@gmail.com>
Date: Wed, 8 Jul 2015 20:46:52 -0400
Subject: Initial commit

---
 math/slalib/dav2m.f | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 math/slalib/dav2m.f

(limited to 'math/slalib/dav2m.f')

diff --git a/math/slalib/dav2m.f b/math/slalib/dav2m.f
new file mode 100644
index 00000000..7eb1f68b
--- /dev/null
+++ b/math/slalib/dav2m.f
@@ -0,0 +1,84 @@
+      SUBROUTINE slDAVM (AXVEC, RMAT)
+*+
+*     - - - - - -
+*      D A V M
+*     - - - - - -
+*
+*  Form the rotation matrix corresponding to a given axial vector.
+*  (double precision)
+*
+*  A rotation matrix describes a rotation about some arbitrary axis,
+*  called the Euler axis.  The "axial vector" supplied to this routine
+*  has the same direction as the Euler axis, and its magnitude is the
+*  amount of rotation in radians.
+*
+*  Given:
+*    AXVEC  d(3)     axial vector (radians)
+*
+*  Returned:
+*    RMAT   d(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.
+*
+*  Last revision:   26 November 2005
+*
+*  Copyright P.T.Wallace.  All rights reserved.
+*
+*  License:
+*    This program is free software; you can redistribute it and/or modify
+*    it under the terms of the GNU General Public License as published by
+*    the Free Software Foundation; either version 2 of the License, or
+*    (at your option) any later version.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU General Public License for more details.
+*
+*    You should have received a copy of the GNU General Public License
+*    along with this program (see SLA_CONDITIONS); if not, write to the
+*    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+*    Boston, MA  02110-1301  USA
+*
+*  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
+*-
+
+      IMPLICIT NONE
+
+      DOUBLE PRECISION AXVEC(3),RMAT(3,3)
+
+      DOUBLE PRECISION X,Y,Z,PHI,S,C,W
+
+
+
+*  Rotation 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 = 1D0-C
+
+*  Euler axis - direction of axial vector (perhaps null)
+      IF (PHI.NE.0D0) 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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