From b8ba202301e5e4cf392a827c9bb8ebf2265de99f Mon Sep 17 00:00:00 2001
From: marcandre <marcandre@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Sun, 6 Apr 2014 17:45:54 +0000
Subject: * lib/matrix.rb: Add first_minor [fix GH-568]   Patch by gogotanaka

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45527 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 NEWS                       |  5 +++++
 lib/matrix.rb              | 29 +++++++++++++++++++++++++++++
 test/matrix/test_matrix.rb | 12 ++++++++++++
 3 files changed, 46 insertions(+)

diff --git a/NEWS b/NEWS
index 244e79a0ae..4e344227bb 100644
--- a/NEWS
+++ b/NEWS
@@ -27,6 +27,11 @@ with all sufficient information, see the ChangeLog file.
     * Most symbols which are returned by String#to_sym and
       String#intern are GC-able.
 
+* Matrix
+  * New methods:
+    * Matrix#first_minor(row, column) returns the submatrix obtained
+      by deleting the specified row and column.
+
 === Core classes compatibility issues (excluding feature bug fixes)
 
 * IO
diff --git a/lib/matrix.rb b/lib/matrix.rb
index e0995c394f..7502e6ef8b 100644
--- a/lib/matrix.rb
+++ b/lib/matrix.rb
@@ -58,6 +58,7 @@ end
 # * #each_with_index
 # * #find_index
 # * #minor(*param)
+# * #first_minor(row, column)
 #
 # Properties of a matrix:
 # * #diagonal?
@@ -590,6 +591,34 @@ class Matrix
     new_matrix rows, [column_count - from_col, size_col].min
   end
 
+  #
+  # Returns the submatrix obtained by deleting the specified row and column.
+  #
+  #   Matrix.diagonal(9, 5, -3, 4).first_minor(1, 2)
+  #     => 9 0 0
+  #        0 0 0
+  #        0 0 4
+  #
+  def first_minor(row, column)
+    raise RuntimeError, "first_minor of empty matrix is not defined" if empty?
+
+    unless 0 <= row && row < row_count
+      raise ArgumentError, "invalid row (#{row.inspect} for 0..#{row_count - 1})"
+    end
+
+    unless 0 <= column && column < column_count
+      raise ArgumentError, "invalid column (#{column.inspect} for 0..#{column_count - 1})"
+    end
+
+    arrays = to_a
+    arrays.delete_at(row)
+    arrays.each do |array|
+      array.delete_at(column)
+    end
+
+    new_matrix arrays, column_count - 1
+  end
+
   #--
   # TESTING -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
   #++
diff --git a/test/matrix/test_matrix.rb b/test/matrix/test_matrix.rb
index 575b7b0cd6..2412f00822 100644
--- a/test/matrix/test_matrix.rb
+++ b/test/matrix/test_matrix.rb
@@ -250,6 +250,18 @@ class TestMatrix < Test::Unit::TestCase
     assert_raise(ArgumentError) { @m1.minor(0) }
   end
 
+  def test_first_minor
+    assert_equal(Matrix.empty(0, 0), Matrix[[1]].first_minor(0, 0))
+    assert_equal(Matrix.empty(0, 2), Matrix[[1, 4, 2]].first_minor(0, 1))
+    assert_equal(Matrix[[1, 3]], @m1.first_minor(1, 1))
+    assert_equal(Matrix[[4, 6]], @m1.first_minor(0, 1))
+    assert_equal(Matrix[[1, 2]], @m1.first_minor(1, 2))
+    assert_raise(RuntimeError) { Matrix.empty(0, 0).first_minor(0, 0) }
+    assert_raise(ArgumentError) { @m1.first_minor(4, 0) }
+    assert_raise(ArgumentError) { @m1.first_minor(0, -1) }
+    assert_raise(ArgumentError) { @m1.first_minor(-1, 4) }
+  end
+
   def test_regular?
     assert(Matrix[[1, 0], [0, 1]].regular?)
     assert(Matrix[[1, 0, 0], [0, 1, 0], [0, 0, 1]].regular?)
-- 
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