diff --git a/PHPSkills/Numerics/Matrix.php b/PHPSkills/Numerics/Matrix.php
index 568f867..7c14209 100644
--- a/PHPSkills/Numerics/Matrix.php
+++ b/PHPSkills/Numerics/Matrix.php
@@ -159,7 +159,7 @@ class Matrix
         // The idea is that it's the transpose of the cofactors
         $result = array();
 
-        for ($currentColumn = 0; $currentColumn < $this->_columns; $currentColumn++)
+        for ($currentColumn = 0; $currentColumn < $this->_columnCount; $currentColumn++)
         {
             for ($currentRow = 0; $currentRow < $this->_rowCount; $currentRow++)
             {
@@ -185,7 +185,7 @@ class Matrix
         return self::scalarMultiply($determinantInverse, $adjugate);
     }
 
-    public static function scalarMultiply($scalar, $matrix)
+    public static function scalarMultiply($scalarValue, $matrix)
     {
         $rows = $matrix->getRowCount();
         $columns = $matrix->getColumnCount();
@@ -393,6 +393,20 @@ class DiagonalMatrix extends Matrix
         
         parent::__construct($rowCount, $colCount);
         
+        for($currentRow = 0; $currentRow < $rowCount; $currentRow++)
+        {
+            for($currentCol = 0; $currentCol < $colCount; $currentCol++)
+            {
+                if($currentRow == $currentCol)
+                {
+                    $this->setValue($currentRow, $currentCol, $diagonalValues[$currentRow]);
+                }
+                else
+                {
+                    $this->setValue($currentRow, $currentCol, 0);
+                }                
+            }
+        }
         for($i = 0; $i < $diagonalCount; $i++)
         {
             $this->setValue($i, $i, $diagonalValues[$i]);
diff --git a/UnitTests/Numerics/MatrixTest.php b/UnitTests/Numerics/MatrixTest.php
index c351d39..881d655 100644
--- a/UnitTests/Numerics/MatrixTest.php
+++ b/UnitTests/Numerics/MatrixTest.php
@@ -6,6 +6,7 @@ require_once(dirname(__FILE__) . '/../../PHPSkills/Numerics/Matrix.php');
 
 use \PHPUnit_Framework_TestCase;
 use Moserware\Numerics\Matrix;
+use Moserware\Numerics\IdentityMatrix;
 use Moserware\Numerics\SquareMatrix;
 
 class MatrixTest extends PHPUnit_Framework_TestCase
@@ -129,10 +130,67 @@ class MatrixTest extends PHPUnit_Framework_TestCase
 
         $this->assertTrue($g->equals($h));
     }
+
+    public function testAdjugate()
+    {
+        // From Wikipedia: http://en.wikipedia.org/wiki/Adjugate_matrix
+        $a = new SquareMatrix(1, 2,
+                              3, 4);
+
+        $b = new SquareMatrix( 4, -2,
+                              -3,  1);
+
+        $this->assertTrue($b->equals($a->getAdjugate()));
+
+
+        $c = new SquareMatrix(-3,  2, -5,
+                              -1,  0, -2,
+                               3, -4,  1);
+
+        $d = new SquareMatrix(-8, 18, -4,
+                              -5, 12, -1,
+                               4, -6,  2);
+
+        $this->assertTrue($d->equals($c->getAdjugate()));
+    }
+
+    public function testInverse()
+    {
+        // see http://www.mathwords.com/i/inverse_of_a_matrix.htm
+        $a = new SquareMatrix(4, 3,
+                              3, 2);
+
+        $b = new SquareMatrix(-2,  3,
+                               3, -4);
+
+        $aInverse = $a->getInverse();
+        $this->assertTrue($b->equals($aInverse));
+
+        $identity2x2 = new IdentityMatrix(2);
+
+        $aaInverse = Matrix::multiply($a, $aInverse);
+        $this->assertTrue($identity2x2->equals($aaInverse));
+
+        $c = new SquareMatrix(1, 2, 3,
+                              0, 4, 5,
+                              1, 0, 6);
+
+        $cInverse = $c->getInverse();
+        $d = Matrix::scalarMultiply((1.0 / 22), new SquareMatrix(24, -12, -2,
+                                                                  5,   3, -5,
+                                                                 -4,   2,  4));
+
+
+        $this->assertTrue($d->equals($cInverse));
+        $identity3x3 = new IdentityMatrix(3);
+
+        $ccInverse = Matrix::multiply($c, $cInverse);
+        $this->assertTrue($identity3x3->equals($ccInverse));
+    }
 }
 
 $testSuite = new \PHPUnit_Framework_TestSuite();
-$testSuite->addTest( new MatrixTest("testEquals"));
+$testSuite->addTest( new MatrixTest("testInverse"));
 \PHPUnit_TextUI_TestRunner::run($testSuite);
 
 ?>