* lib/matrix.rb: Add Vector.basis.

Based on patch by gogo tanaka [#10072]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47833 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Wed Oct  8 04:29:21 2014  Marc-Andre Lafortune  <ruby-core@marc-andre.ca>
+
+	* lib/matrix.rb: Add Vector.basis.
+	  Based on patch by gogo tanaka [#10072]
+
 Tue Oct  7 23:40:16 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* signal.c (rb_f_kill): get rid of deadlock as unhandled and

NEWS

@@ -84,6 +84,7 @@ with all sufficient information, see the ChangeLog file.
       which is obtained by multiplying the first minor by (-1)**(row + column).
     * hstack and vstack are new instance and class methods to stack matrices
       horizontally and vertically.
+    * Vector.basis(size:, index:) returns the specified basis vector
 
 * Method
   * New methods:

lib/matrix.rb

@@ -1624,6 +1624,7 @@ end
 # To create a Vector:
 # * Vector.[](*array)
 # * Vector.elements(array, copy = true)
+# * Vector.basis(size: n, index: k)
 #
 # To access elements:
 # * #[](i)
@@ -1685,6 +1686,19 @@ class Vector
     new convert_to_array(array, copy)
   end
 
+  #
+  # Returns a standard basis +n+-vector, where k is the index.
+  #
+  #    Vector.basis(size:, index:) # => Vector[0, 1, 0]
+  #
+  def Vector.basis(size:, index:)
+    raise ArgumentError, "invalid size (#{size} for 1..)" if size < 1
+    raise ArgumentError, "invalid index (#{index} for 0...#{size})" unless 0 <= index && index < size
+    array = Array.new(size, 0)
+    array[index] = 1
+    new convert_to_array(array, false)
+  end
+
   #
   # Vector.new is private; use Vector[] or Vector.elements to create.
   #

test/matrix/test_vector.rb

@@ -10,6 +10,15 @@ class TestVector < Test::Unit::TestCase
     @w1 = Vector[2,3,4]
   end
 
+  def test_basis
+    assert_equal(Vector[1, 0, 0], Vector.basis(size: 3, index: 0))
+    assert_raise(ArgumentError) { Vector.basis(size: -1, index: 2) }
+    assert_raise(ArgumentError) { Vector.basis(size: 4, index: -1) }
+    assert_raise(ArgumentError) { Vector.basis(size: 3, index: 3) }
+    assert_raise(ArgumentError) { Vector.basis(size: 3) }
+    assert_raise(ArgumentError) { Vector.basis(index: 3) }
+  end
+
   def test_identity
     assert_same @v1, @v1
     assert_not_same @v1, @v2