public function testMap()
{
$A = MatrixFactory::create([[1, 2, 3], [4, 5, 6], [7, 8, 9]]);
$doubler = function ($x) {
return $x * 2;
};
$R = $A->map($doubler);
$E = MatrixFactory::create([[2, 4, 6], [8, 10, 12], [14, 16, 18]]);
$this->assertEquals($E, $R);
}