MCordingley\LinearAlgebra\Matrix::trace PHP Method

    public function trace() : float
    {
        $this->checkSquare();
        $trace = 0;
        for ($i = 0, $rows = $this->getRowCount(); $i < $rows; $i++) {
            $trace += $this->get($i, $i);
        }
        return $trace;
    }

 public function testTrace()
 {
     $matrix = new Matrix([[1, 2, 3], [0, 1, 4], [5, 6, 0]]);
     static::assertEquals(2, $matrix->trace());
 }