sdp::MatrixMask Class Reference

Implements a matrix bit-mask. More...

#include <matrixmask.h>

Classes
struct	Position
	A position in the mask. More...

Public Types
typedef std::list< Position > ::const_iterator	const_iterator
	Constant iterator.

Public Member Functions
	MatrixMask (int nn)
	Constructs an nn by nn mask with all entries off.
	MatrixMask (int mm, int nn)
	Constructs an mm by nn mask with all entries off.
	MatrixMask (const MatrixMask &other)
	Copy constructor.
MatrixMask &	operator= (const MatrixMask &)=delete
	Assignment is not implemented.
int	on_count () const
	Returns number of on positions.
int	num_rows () const
	Returns number of rows.
int	num_cols () const
	Returns number of columns.
bool	is_on (int i, int j) const
	Returns true if entry (i, j) of the mask is on.
void	turn_on (int i, int j)
	Turns on entry (i, j) of the mask.
void	turn_off (int i, int j)
	Turns off entry (i, j) of the mask.
void	clear ()
	Clears the whole mask, turning off all entries.
const_iterator	begin () const
	Returns iterator to the beginning of the list of on positions.
const_iterator	end () const
	Returns past-the-end iterator to the list of on positions.

Friends
class	shared_ref< MatrixMask >
class	const_shared_ref< MatrixMask >

Detailed Description

Implements a matrix bit-mask.

A MatrixMask contains an m by n matrix of bits. It can be used, for instance, to store the nonzero positions of a matrix. Some functions use a MatrixMask in order to efficiently deal with sparse matrices.

A MatrixMask also contains a list of the entries that are on. So it is efficient to iterate over all the entries turned on.

Each entry of the mask occupies only one bit, so that even large masks do not use up too much space. So it is efficient to use masks of large size. Notice however that, if too many positions are on, then the list of positions that are turned on might come to occupy a large amount of memory. So masks are better kept sparse.

MatrixMask implements the shared reference mechanism. To understand how it works, see the documentation of shared_ref, const_shared_ref, and Matrix for an example.

Complexity

Turning a position on and checking whether a position is on or off takes constant time. Turning a position off takes at the moment time linear time on the number of positions that are on. Iteration through the list of positions that are on takes constant time per position turned on.

Iteration

MatrixMask supports both C++ and C++11 style iteration. One iterates over a list of positions, i.e., instances of struct MatrixMask::Position, containing the nonzero entries of the mask.

Todo:

In the future, it might be wise to change the list of positions on_pos to a vector. This might save memory.

---

The documentation for this class was generated from the following file:

• include/sdpsl/matrixmask.h