From 649f646fa8d6f39dca6558ed8e44fb4913c9e76a Mon Sep 17 00:00:00 2001
From: Doug Coleman <erg@trifocus.net>
Date: Fri, 21 Oct 2005 18:51:49 +0000
Subject: [PATCH] Move quaternions from library/math to contrib/math

---
 contrib/math/quaternions.factor | 78 +++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 contrib/math/quaternions.factor

diff --git a/contrib/math/quaternions.factor b/contrib/math/quaternions.factor
new file mode 100644
index 0000000000..d2fbf5bcff
--- /dev/null
+++ b/contrib/math/quaternions.factor
@@ -0,0 +1,78 @@
+! Copyright (C) 2005 Slava Pestov.
+! See http://factor.sf.net/license.txt for BSD license.
+
+! Everybody's favorite non-commutative skew field, the
+! quaternions!
+
+! Quaternions are represented as pairs of complex numbers,
+! using the identity: (a+bi)+(c+di)j = a+bi+cj+dk.
+USING: arrays kernel math sequences ;
+IN: math-internals
+
+: 2q [ first2 ] 2apply ; inline
+
+: q*a 2q swapd ** >r * r> - ; inline
+
+: q*b 2q >r ** swap r> * + ; inline
+
+IN: math
+
+: q* ( u v -- u*v )
+    #! Multiply quaternions.
+    [ q*a ] 2keep q*b 2array ;
+
+: qconjugate ( u -- u' )
+    #! Quaternion conjugate.
+    first2 neg >r conjugate r> 2array ;
+
+: qrecip ( u -- 1/u )
+    #! Quaternion inverse.
+    qconjugate dup norm-sq v/n ;
+
+: q/ ( u v -- u/v )
+    #! Divide quaternions.
+    qrecip q* ;
+
+: q*n ( q n -- q )
+    #! Note: you will get the wrong result if you try to
+    #! multiply a quaternion by a complex number on the right
+    #! using v*n. Use this word instead. Note that v*n with a
+    #! quaternion and a real is okay.
+    conjugate v*n ;
+
+: c>q ( c -- q )
+    #! Turn a complex number into a quaternion.
+    0 2array ;
+
+: v>q ( v -- q )
+    #! Turn a 3-vector into a quaternion with real part 0.
+    first3 rect> >r 0 swap rect> r> 2array ;
+
+: q>v ( q -- v )
+    #! Get the vector part of a quaternion, discarding the real
+    #! part.
+    first2 >r imaginary r> >rect 3array ;
+
+: cross ( u v -- u*v )
+    #! Cross product of two 3-vectors can be computed using
+    #! quaternion multiplication.
+    [ v>q ] 2apply q* q>v ;
+
+! Zero
+: q0 @{ 0 0 }@ ;
+
+! Units
+: q1 @{ 1 0 }@ ;
+: qi @{ #{ 0 1 }# 0 }@ ;
+: qj @{ 0 1 }@ ;
+: qk @{ 0 #{ 0 1 }# }@ ;
+
+! Euler angles -- see
+! http://www.mathworks.com/access/helpdesk/help/toolbox/aeroblks/euleranglestoquaternions.html
+
+: (euler) ( theta unit -- q )
+    >r -0.5 * dup cos c>q swap sin r> n*v v- ;
+
+: euler ( phi theta psi -- q )
+    qk (euler) >r qj (euler) >r qi (euler) r> q* r> q* ;
+