commit 5bd5f93da54d44aff6d22072252a76947d01a996
Author: Lito Nicolai <lito.nicolai@gmail.com>
Date:   Sun Feb 15 10:44:53 2015 -0800

    Matrix#inverse returns matrix of integers whenever possible

diff --git a/ChangeLog b/ChangeLog
index 8e7a96b..61dc486 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Mon Feb 16 03:37:45 2015  Lito Nicolai <lito.nicolai@gmail.com>
+
+      * lib/matrix.rb (inverse_from): return a matrix of integers
+      whenever possible
+
+      * test/matrix/test_matrix.rb (test_inverse): test for fix
+
 Sat Feb  7 22:13:08 2015  Masaki Suketa <masaki.suketa@nifty.ne.jp>
 
 	* test/win32ole/test_win32ole_record.rb: remove test using .NET
diff --git a/lib/matrix.rb b/lib/matrix.rb
index fb98d09..e79c361 100644
--- a/lib/matrix.rb
+++ b/lib/matrix.rb
@@ -1103,10 +1103,24 @@ class Matrix
         @rows[k][j] = @rows[k][j].quo(akk)
       end
     end
-    self
+    integral_from_rational(self)
   end
   private :inverse_from
 
+  def integral_from_rational(src) # :nodoc:
+    n = Matrix.build(src.row_count) do |i , j|
+      elem = src[i, j]
+      if elem.is_a?(Rational) && elem.denominator == 1
+         elem.to_i
+      else
+        break
+      end
+    end
+
+    n.nil? ? src : n
+  end
+  private :integral_from_rational
+
   #
   # Matrix exponentiation.
   # Equivalent to multiplying the matrix by itself N times.
diff --git a/test/matrix/test_matrix.rb b/test/matrix/test_matrix.rb
index 3fdef3b..d8b95ec 100644
--- a/test/matrix/test_matrix.rb
+++ b/test/matrix/test_matrix.rb
@@ -174,8 +174,15 @@ class TestMatrix < Test::Unit::TestCase
 
   def test_inverse
     assert_equal(Matrix.empty(0, 0), Matrix.empty.inverse)
-    assert_equal(Matrix[[-1, 1], [0, -1]], Matrix[[-1, -1], [0, -1]].inverse)
+    assert Matrix[[-1, 1], [0, -1]].eql? Matrix[[-1, -1], [0, -1]].inverse
+    assert Matrix[[1, 2], [3, 4]].inverse.eql?(
+      Matrix[[Rational(-2), Rational(1)],
+             [Rational(3, 2), Rational(-1, 2)]]
+    )
     assert_raise(ExceptionForMatrix::ErrDimensionMismatch) { @m1.inverse }
+    assert_raise(ExceptionForMatrix::ErrNotRegular) {
+      Matrix[[0, 0], [0, 0]].inverse
+    }
   end
 
   def test_determinant