jsat.linear

Class SubMatrix

java.lang.Object

jsat.linear.Matrix

jsat.linear.GenericMatrix

jsat.linear.SubMatrix

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable

public class SubMatrix
extends GenericMatrix

This class allows for the selection of an area of a matrix to operate on independently. Mutable matrix operations perform on this sub matrix, will be visible in the base matrix given. This allows for easy implementation of blocking algorithms, but care must be taken to not create and use two sub matrices that overlap and are altered simultaneously.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
SubMatrix(Matrix baseMatrix, int firstRow, int firstColumn, int toRow, int toCol) Creates a new matrix that is a sub view of the given base matrix.

Method Summary

Modifier and Type	Method and Description
void	changeSize(int newRows, int newCols) This method alters the size of a matrix, either adding or subtracting rows from the internal structure of the matrix.
int	cols() Returns the number of columns stored in this matrix
double	get(int i, int j) Returns the value stored at at the matrix position Ai,j
Matrix	getBaseMatrix() Returns the matrix that is the base for this sub matrix.
Vec	getColumnView(int j) Obtains a vector that is backed by this, at very little memory cost.
int	getFirstColumn() Returns the column offset used from the base matrix
int	getFirstRow() Returns the row offset used from the base matrix
Vec	getRowView(int r) Obtains a vector that is backed by this, at very little memory cost.
boolean	isSparce() Returns true if the matrix is sparse, false otherwise
int	rows() Returns the number of rows stored in this matrix
void	set(int i, int j, double value) Sets the value stored at at the matrix position Ai,j

Methods inherited from class jsat.linear.GenericMatrix

clone, lup, lup, multiply, multiply, multiply, multiplyTranspose, multiplyTranspose, mutableAdd, mutableAdd, mutableAdd, mutableAdd, mutableMultiply, mutableMultiply, mutableTranspose, qr, qr, swapRows, transpose, transposeMultiply, transposeMultiply, transposeMultiply, zeroOut

Methods inherited from class jsat.linear.Matrix

add, add, add, add, canBeMutated, canMultiply, copyTo, diag, diagMult, diagMult, equals, equals, eye, getColumn, getRow, increment, isSquare, isSymmetric, isSymmetric, multiply, multiply, multiply, multiply, multiply, multiplyTranspose, multiplyTranspose, mutableAdd, mutableAdd, mutableSubtract, mutableSubtract, mutableSubtract, mutableSubtract, mutableSubtract, mutableSubtract, nnz, OuterProductUpdate, OuterProductUpdate, pascal, random, sameDimensions, subtract, subtract, subtract, subtract, toString, transpose, transposeMultiply, transposeMultiply, transposeMultiply, updateRow

Methods inherited from class java.lang.Object

getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

SubMatrix

public SubMatrix(Matrix baseMatrix,
                 int firstRow,
                 int firstColumn,
                 int toRow,
                 int toCol)

Creates a new matrix that is a sub view of the given base matrix.

Parameters:

baseMatrix - the base matrix to get a view of

firstRow - the first row to consider as part of the sub matrix, starting from 0 inclusive

firstColumn - the first column to consider as part of the sub matrix, starting from 0 inclusive

toRow - the last row from the base matrix to consider, exclusive

toCol - the last column from the base matrix to consider, exclusive

Method Detail

getBaseMatrix

public Matrix getBaseMatrix()

Returns the matrix that is the base for this sub matrix.

Returns:

the matrix that is the base for this sub matrix.

getFirstRow

public int getFirstRow()

Returns the row offset used from the base matrix

Returns:

the row offset used from the base matrix

getFirstColumn

public int getFirstColumn()

Returns the column offset used from the base matrix

Returns:

the column offset used from the base matrix

get

public double get(int i,
                  int j)

Description copied from class: Matrix

Returns the value stored at at the matrix position A_i,j

Specified by:

get in class Matrix

Parameters:

i - the row, starting from 0

j - the column, starting from 0

Returns:

the value at A_i,j

set

public void set(int i,
                int j,
                double value)

Description copied from class: Matrix

Sets the value stored at at the matrix position A_i,j

Specified by:

set in class Matrix

Parameters:

i - the row, starting from 0

j - the column, starting from 0

value - the value to place at A_i,j

getRowView

public Vec getRowView(int r)

Description copied from class: Matrix

Obtains a vector that is backed by this, at very little memory cost. Mutations to this vector will alter the values stored in the matrix, and vice versa.

Overrides:

getRowView in class Matrix

Parameters:

r - the row to obtain a view of

Returns:

a vector backed by the specified row of the matrix

getColumnView

public Vec getColumnView(int j)

Description copied from class: Matrix

Obtains a vector that is backed by this, at very little memory cost. Mutations to this vector will alter the values stored in the matrix, and vice versa.

Overrides:

getColumnView in class Matrix

Parameters:

j - the column to obtain a view of

Returns:

a vector backed by the specified row of the matrix

rows

public int rows()

Description copied from class: Matrix

Returns the number of rows stored in this matrix

Specified by:

rows in class Matrix

Returns:

the number of rows stored in this matrix

cols

public int cols()

Description copied from class: Matrix

Returns the number of columns stored in this matrix

Specified by:

cols in class Matrix

Returns:

the number of columns stored in this matrix

isSparce

public boolean isSparce()

Description copied from class: Matrix

Returns true if the matrix is sparse, false otherwise

Specified by:

isSparce in class Matrix

Returns:

true if the matrix is sparse, false otherwise

changeSize

public void changeSize(int newRows,
                       int newCols)

This method alters the size of a matrix, either adding or subtracting rows from the internal structure of the matrix. Every resize call may cause a new allocation internally, and should not be called for excessive changing of a matrix. All added rows/ columns will have values of zero. If a row / column is removed, it is always the bottom/right most row / column removed. Values of the removed rows / columns will be lost.

When a SubMatrix attempts to change size, it may alter the values of the underlying matrix in an unusual way. If the base matrix is large enough to hold the changed size, then the values in the underlying matrix that this SubMatrix is expanding to encompass will be set to zero. If the underlying matrix is not large enough, change size will be called upon it as well.
When decreasing the number of rows / columns, the SubMatrix will always reduce its view - but never shrink the underling matrix that the view is of.
To expand the size of a SubMatrix without zeroing out the new values, create a new SubMatrix object.

Specified by:

changeSize in class Matrix

Parameters:

newRows - the new number of rows, must be positive

newCols - the new number of columns, must be positive.