From f0a7984f39f552363a03b6a2bb62b8b5ae65e218 Mon Sep 17 00:00:00 2001
From: Povilas Susinskas <povilas.susinskas@gmail.com>
Date: Wed, 15 Feb 2017 11:09:16 +0200
Subject: [PATCH] Check if matrix is singular doing inverse (#49)

* Check if matrix is singular doing inverse

* add return bool type
---
 src/Phpml/Exception/MatrixException.php |  8 ++++++++
 src/Phpml/Math/Matrix.php               | 12 ++++++++++++
 tests/Phpml/Math/MatrixTest.php         | 14 ++++++++++++++
 3 files changed, 34 insertions(+)

diff --git a/src/Phpml/Exception/MatrixException.php b/src/Phpml/Exception/MatrixException.php
index 9aaa43a..2815804 100644
--- a/src/Phpml/Exception/MatrixException.php
+++ b/src/Phpml/Exception/MatrixException.php
@@ -21,4 +21,12 @@ class MatrixException extends \Exception
     {
         return new self('Column out of range');
     }
+
+    /**
+     * @return MatrixException
+     */
+    public static function singularMatrix()
+    {
+       return new self('Matrix is singular');
+    }
 }
diff --git a/src/Phpml/Math/Matrix.php b/src/Phpml/Math/Matrix.php
index 6485a7d..39f5c5a 100644
--- a/src/Phpml/Math/Matrix.php
+++ b/src/Phpml/Math/Matrix.php
@@ -233,6 +233,10 @@ class Matrix
             throw MatrixException::notSquareMatrix();
         }
 
+        if ($this->isSingular()) {
+            throw MatrixException::singularMatrix();
+        }
+
         $newMatrix = [];
         for ($i = 0; $i < $this->rows; ++$i) {
             for ($j = 0; $j < $this->columns; ++$j) {
@@ -271,4 +275,12 @@ class Matrix
 
         return new self($newMatrix, false);
     }
+
+    /**
+     * @return bool
+     */
+    public function isSingular() : bool
+    {
+        return 0 == $this->getDeterminant();
+    }
 }
diff --git a/tests/Phpml/Math/MatrixTest.php b/tests/Phpml/Math/MatrixTest.php
index b4adc76..48a6fe9 100644
--- a/tests/Phpml/Math/MatrixTest.php
+++ b/tests/Phpml/Math/MatrixTest.php
@@ -141,6 +141,20 @@ class MatrixTest extends TestCase
         $matrix->inverse();
     }
 
+    /**
+     * @expectedException \Phpml\Exception\MatrixException
+     */
+    public function testThrowExceptionWhenInverseIfMatrixIsSingular()
+    {
+       $matrix = new Matrix([
+          [0, 0, 0],
+          [0, 0, 0],
+          [0, 0, 0],
+       ]);
+
+       $matrix->inverse();
+    }
+
     public function testInverseMatrix()
     {
         //http://ncalculators.com/matrix/inverse-matrix.htm