Implemented matrix rank

Author: andrewdalpino

src/Matrix.php

@@ -645,6 +645,29 @@ public function det() : float
         return (-1.) ** $swaps * $dHat;
     }
 
+    /**
+     * Calculate the rank of the matrix i.e the number of pivots
+     * in its reduced row echelon form.
+     * 
+     * @return int
+     */
+    public function rank() : int
+    {
+        $pivots = 0;
+
+        foreach ($this->rref() as $row) {
+            foreach ($row as $value) {
+                if ($value != 0) {
+                    $pivots++;
+
+                    continue 2;
+                }
+            }
+        }
+
+        return $pivots;
+    }
+
     /**
      * Return the elementwise reciprocal of the matrix.
      *

tests/MatrixTest.php

@@ -350,6 +350,13 @@ public function test_det()
         $this->assertEquals(-544., $this->c->det());
     }
 
+    public function test_rank()
+    {
+        $this->assertEquals(3, $this->a->rank());
+        $this->assertEquals(1, $this->b->rank());
+        $this->assertEquals(3, $this->c->rank());
+    }
+
     public function test_reciprocal()
     {
         $z = $this->a->reciprocal();