/*
* Copyright 2011 David Jurgens
*
* This file is part of the S-Space package and is covered under the terms and
* conditions therein.
*
* The S-Space package is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as published
* by the Free Software Foundation and distributed hereunder to you.
*
* THIS SOFTWARE IS PROVIDED "AS IS" AND NO REPRESENTATIONS OR WARRANTIES,
* EXPRESS OR IMPLIED ARE MADE. BY WAY OF EXAMPLE, BUT NOT LIMITATION, WE MAKE
* NO REPRESENTATIONS OR WARRANTIES OF MERCHANT- ABILITY OR FITNESS FOR ANY
* PARTICULAR PURPOSE OR THAT THE USE OF THE LICENSED SOFTWARE OR DOCUMENTATION
* WILL NOT INFRINGE ANY THIRD PARTY PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER
* RIGHTS.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package edu.ucla.sspace.matrix;
import edu.ucla.sspace.vector.DenseVector;
import edu.ucla.sspace.vector.DoubleVector;
import edu.ucla.sspace.vector.Vector;
import edu.ucla.sspace.vector.Vectors;
/**
* A symmetric dense matrix that only stores the values of the lower triangular.
* This class only records changes values where row > col. For all other
* values, the row and column values are swapped and then the backing matrix is
* updated.
*
* </p>
*
* The primary benfit of this class is for storing large symmetric matrices in
* half of the memory.
*
* @author David Jurgens
*/
public class SymmetricMatrix extends AbstractMatrix
implements java.io.Serializable {
private static final long serialVersionUID = 1L;
private final double[][] values;
private final int rows;
private final int columns;
/**
* Constructs a new {@link SymmetricMatrix} with the specified dimensions.
*/
public SymmetricMatrix(int rows, int columns) {
this.rows = rows;
this.columns = columns;
values = new double[rows][];
for (int r = 0; r < rows; ++r)
values[r] = new double[r+1];
}
/**
* {@inheritDoc}
*/
public int columns() {
return columns;
}
/**
* {@inheritDoc}
*/
@Override public double get(int row, int column) {
// Swap the ordering so only the lower triangular is read
if (column > row) {
int tmp = column;
column = row;
row = tmp;
}
return values[row][column];
}
/**
* {@inheritDoc}
*/
public DoubleVector getColumnVector(int column) {
DenseVector col = new DenseVector(rows);
for (int r = 0; r < rows; ++r)
col.set(r, get(r, column));
return col;
}
/**
* {@inheritDoc}
*/
public DoubleVector getRowVector(int row) {
DenseVector rowVec = new DenseVector(columns);
for (int c = 0; c < columns; ++c)
rowVec.set(c, get(row, c));
return rowVec;
}
/**
* {@inheritDoc}
*/
public int rows() {
return rows;
}
/**
* {@inheritDoc}
*/
@Override public void set(int row, int column, double val) {
// Swap the ordering so only the lower triangular is written to
if (column > row) {
int tmp = column;
column = row;
row = tmp;
}
values[row][column] = val;
}
}