Added trace feature to Matrix Class

See #10

Author: malenkiki

src/Malenki/Math/Matrix.php

@@ -104,7 +104,7 @@ public function __get($name)
             return $this->isSquare();
         }
 
-        if(in_array($name, array('cofactor', 'adjugate', 'inverse', 'det', 'determinant', 'transpose')))
+        if(in_array($name, array('cofactor', 'adjugate', 'inverse', 'det', 'trace', 'determinant', 'transpose')))
         {
             return $this->$name();
         }
@@ -691,6 +691,23 @@ public function det()
         }
     }
 
+    public function trace()
+    {
+        if(!$this->isSquare())
+        {
+            throw new \RuntimeException('Cannot compute trace of non square matrix!');
+        }
+
+        $int = 0;
+
+        for($i = 0; $i < $this->size->rows; $i++)
+        {
+            $int += $this->get($i, $i);
+        }
+
+        return $int;
+    }
+
 
     public function determinant()
     {

tests/MatrixTest.php

@@ -311,4 +311,23 @@ public function testToString()
         $this->assertEquals("1  2+i   3\n4    5  60", sprintf('%s', $m));
     }
 
+    public function testGettingTraceShouldSuccess()
+    {
+        $m = new Matrix(2, 2);
+        $m->populate(array(1, 2, 3, 4));
+
+        $this->assertEquals(5, $m->trace());
+        $this->assertEquals(5, $m->trace);
+    }
+    
+    /**
+     * @expectedException \RuntimeException
+     */
+    public function testGettingTraceiFromNonSquareMatrixShouldFail()
+    {
+        $m = new Matrix(2, 3);
+        $m->populate(array(1, 2, 3, 4, 5, 6));
+
+        $m->trace();
+    }
 }