* 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

1 files changed, 14 insertions, 0 deletions

diff --git a/lib/matrix.rb b/lib/matrix.rb
index 81834ab898..054c197b52 100644
--- a/lib/matrix.rb
+++ b/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)
@@ -1686,6 +1687,19 @@ class Vector
   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.
   #
   def initialize(array)