/**
* Get the L of the composition L^T*D*L.
*
* @return matrix L
*/
public function getL()
{
$L = $this->_matrix->copy();
// L is the lower triangular matrix.
for ($i = 0; $i < $L->rows(); $i++) {
for ($j = $i; $j < $L->columns(); $j++) {
if ($j == $i) {
$L->set($i, $j, 1);
} else {
$L->set($i, $j, 0);
}
}
}
return $L;
}
/**
* Get the U of the decomposition.
*
* @return matrix U
*/
public function getU()
{
$U = $this->_matrix->copy();
for ($i = 0; $i < $U->rows(); $i++) {
for ($j = 0; $j < $i; $j++) {
$U->set($i, $j, 0);
}
}
return $U;
}
/**
* Gets the upper triangular matrix R.
*/
public function getR()
{
$R = $this->_matrix->copy();
$n = min($R->rows(), $R->columns());
for ($i = 0; $i < $R->rows(); $i++) {
for ($j = 0; $j < $i and $j < $n; $j++) {
$R->set($i, $j, 0);
}
}
return $R;
}
/**
* Gets the upper triangular matrix R.
*/
public function getR()
{
$R = $this->_matrix->copy();
for ($i = 0; $i < $R->rows(); $i++) {
for ($j = 0; $j < $i; $j++) {
$R->set($i, $j, 0);
}
}
// Resize R to a square matrix.
$n = min($R->rows(), $R->columns());
return $R->resize($n, $n);
}
/**
* Add to matrices.
*
* @param matrix $a
* @param matrix $b
* @return matrix $a + $b
*/
public static function add($a, $b)
{
new Assertion($a instanceof Matrix, 'Given first matrix not of class Matrix.');
new Assertion($b instanceof Matrix, 'Given second matrix not of class Matrix.');
new Assertion($a->rows() == $b->rows(), 'Given dimensions are not compatible.');
new Assertion($a->columns() == $b->columns(), 'Given dimensions are not compatible.');
$rows = $a->rows();
$columns = $a->columns();
$matrix = $a->copy();
for ($i = 0; $i < $rows; $i++) {
for ($j = 0; $j < $columns; $j++) {
$matrix->set($i, $j, $matrix->get($i, $j) + $b->get($i, $j));
}
}
return $matrix;
}