marcandre	2018-09-16 13:18:50 +0900 (Sun, 16 Sep 2018)

  New Revision: 64761

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=64761

  Log:
    lib/matrix: Fix potential bug of Vector#angle_with
    
    Could happen for some linearly dependent vectors.
    Patch by Vasiliy Petrov. [Fix GH-1803]

  Modified files:
    trunk/lib/matrix.rb
    trunk/test/matrix/test_vector.rb
Index: lib/matrix.rb
===================================================================
--- lib/matrix.rb	(revision 64760)
+++ lib/matrix.rb	(revision 64761)
@@ -2080,7 +2080,7 @@ class Vector https://github.com/ruby/ruby/blob/trunk/lib/matrix.rb#L2080
   end
 
   #
-  # Returns an angle with another vector. Result is within the [0...Math::PI].
+  # Returns an angle with another vector. Result is within the [0..Math::PI].
   #   Vector[1,0].angle_with(Vector[0,1])
   #   # => Math::PI / 2
   #
@@ -2089,8 +2089,12 @@ class Vector https://github.com/ruby/ruby/blob/trunk/lib/matrix.rb#L2089
     Vector.Raise ErrDimensionMismatch if size != v.size
     prod = magnitude * v.magnitude
     raise ZeroVectorError, "Can't get angle of zero vector" if prod == 0
-
-    Math.acos( inner_product(v) / prod )
+    dot = inner_product(v)
+    if dot.abs >= prod
+      dot.positive? ? 0 : Math::PI
+    else
+      Math.acos(dot / prod)
+    end
   end
 
   #--
Index: test/matrix/test_vector.rb
===================================================================
--- test/matrix/test_vector.rb	(revision 64760)
+++ test/matrix/test_vector.rb	(revision 64761)
@@ -223,6 +223,8 @@ class TestVector < Test::Unit::TestCase https://github.com/ruby/ruby/blob/trunk/test/matrix/test_vector.rb#L223
     assert_in_epsilon(Math::PI/2, Vector[1, 0].angle_with(Vector[0, -1]))
     assert_in_epsilon(Math::PI/4, Vector[2, 2].angle_with(Vector[0, 1]))
     assert_in_delta(0.0, Vector[1, 1].angle_with(Vector[1, 1]), 0.00001)
+    assert_equal(Vector[6, 6].angle_with(Vector[7, 7]), 0.0)
+    assert_equal(Vector[6, 6].angle_with(Vector[-7, -7]), Math::PI)
 
     assert_raise(Vector::ZeroVectorError) { Vector[1, 1].angle_with(Vector[0, 0]) }
     assert_raise(Vector::ZeroVectorError) { Vector[0, 0].angle_with(Vector[1, 1]) }

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