public function mult(Matrix $a = NULL, Matrix $b = NULL)
{
$newMatrix = [];
if ($a->getMatrixSizeA() != $b->getMatrixSizeB()) {
throw new IllegalArgumentException();
}
for ($i = 0; $i < $a->getMatrixSizeA(); $i++) {
for ($j = 0; $j < $b->getMatrixSizeB(); $j++) {
for ($k = 0; $k < $a->getMatrixSizeB(); $k++) {
$newMatrix[$i][$j] += $a->getMatrix()[$i][$k] * $b->getMatrix()[$k][$j];
}
}
}
return new Matrix($newMatrix);
}
