* lib/matrix.rb: Fix sign for cross_product [#9499]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46780 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

3 files changed, 12 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index d69a5cf86c..484078e199 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri Jul 11 14:19:14 2014  Marc-Andre Lafortune  <ruby-core@marc-andre.ca>
+
+	* lib/matrix.rb: Fix sign for cross_product [#9499]
+
 Fri Jul 11 11:11:50 2014  Koichi Sasada  <ko1@atdot.net>
 
 	* benchmark/prepare_so_k_nucleotide.rb: use require_relative.
diff --git a/lib/matrix.rb b/lib/matrix.rb
index 1a7519f408..026492b6b8 100644
--- a/lib/matrix.rb
+++ b/lib/matrix.rb
@@ -1811,9 +1811,9 @@ class Vector
   #
   def cross_product(v)
     Vector.Raise ErrDimensionMismatch unless size == v.size && v.size == 3
-    Vector[ v[1]*@elements[2] - v[2]*@elements[1],
-            v[2]*@elements[0] - v[0]*@elements[2],
-            v[0]*@elements[1] - v[1]*@elements[0] ]
+    Vector[ v[2]*@elements[1] - v[1]*@elements[2],
+            v[0]*@elements[2] - v[2]*@elements[0],
+            v[1]*@elements[0] - v[0]*@elements[1] ]
   end
 
   #
diff --git a/test/matrix/test_vector.rb b/test/matrix/test_vector.rb
index 18660df574..ced774c490 100644
--- a/test/matrix/test_vector.rb
+++ b/test/matrix/test_vector.rb
@@ -146,4 +146,9 @@ class TestVector < Test::Unit::TestCase
     v = Vector[Rational(1,2), 0]
     assert_equal(0.5, v.norm)
   end
+
+  def test_cross_product
+    v = Vector[1, 0, 0].cross_product Vector[0, 1, 0]
+    assert_equal(Vector[0, 0, 1], v)
+  end
 end