* lib/matrix.rb: Add Vector#angle_with

Patch by Egunov Dmitriy [#10442]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48505 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Thu Nov 20 02:32:34 2014  Marc-Andre Lafortune  <ruby-core@marc-andre.ca>
+
+	* lib/matrix.rb: Add Vector#angle_with
+	  Patch by Egunov Dmitriy [#10442]
+
 Thu Nov 20 02:10:31 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* parse.y (ripper_flush_string_content, parser_parse_string):

NEWS

@@ -172,6 +172,7 @@ with all sufficient information, see the ChangeLog file.
     * Unary - and + added for Vector and Matrix.
     * Vector#cross_product generalized to arbitrary dimensions.
     * Vector#dot and #cross are aliases for #inner_product and #cross_product.
+    * Vector#angle_with returns the angle with its argument
 
 * Pathname
   * Pathname#/ is aliased to Pathname#+.

lib/matrix.rb

@@ -1699,6 +1699,7 @@ end
 # * #-@
 #
 # Vector functions:
+# * #angle_with(v)
 # * #inner_product(v), dot(v)
 # * #cross_product(v), cross(v)
 # * #collect
@@ -2038,6 +2039,20 @@ class Vector
     self / n
   end
 
+  #
+  # Returns an angle with another vector. Result is within the [0...Math::PI].
+  #   Vector[1,0].angle_with(Vector[0,1])
+  #   # => Math::PI / 2
+  #
+  def angle_with(v)
+    raise TypeError, "Expected a Vector, got a #{v.class}" unless v.is_a?(Vector)
+    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 )
+  end
+
   #--
   # CONVERTING
   #++

test/matrix/test_vector.rb

@@ -182,4 +182,15 @@ class TestVector < Test::Unit::TestCase
     assert_raise(ArgumentError) { Vector[1, 2].cross_product(Vector[2, -1]) }
     assert_raise(Vector::ErrOperationNotDefined) { Vector[1].cross_product }
   end
+
+  def test_angle_with
+    assert_in_epsilon(Math::PI, Vector[1, 0].angle_with(Vector[-1, 0]))
+    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_raise(Vector::ZeroVectorError) { Vector[1, 1].angle_with(Vector[0, 0]) }
+    assert_raise(Vector::ZeroVectorError) { Vector[0, 0].angle_with(Vector[1, 1]) }
+    assert_raise(Matrix::ErrDimensionMismatch) { Vector[1, 2, 3].angle_with(Vector[0, 1]) }
+  end
 end