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A fast and easy to use dense matrix linear algebra library written in Java.

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/*
 * Copyright (c) 2009-2014, Peter Abeles. All Rights Reserved.
 *
 * This file is part of Efficient Java Matrix Library (EJML).
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.ejml.interfaces.decomposition;

import org.ejml.data.ReshapeMatrix64F;

/**
 * 
 * Computes a matrix decomposition such that:

 * 

 * A = U*B*V^T

 * 

 * where A is m by n, U is orthogonal and m by m, B is an m by n bidiagonal matrix, V is orthogonal and n by n.
 * This is used as a first step in computing the SVD of a matrix for the QR algorithm approach.
 * 
 * 
 * A bidiagonal matrix has zeros in every element except for the two diagonals.

 * 

 * b_ij = 0    if i > j or i < j-1

 * 
 *
 *
 * @author Peter Abeles
 */
public interface BidiagonalDecomposition 
        extends DecompositionInterface {

    /**
     * Returns the bidiagonal matrix.
     *
     * @param B If not null the results are stored here, if null a new matrix is created.
     * @return The bidiagonal matrix.
     */
    public T getB( T B , boolean compact );

    /**
     * Returns the orthogonal U matrix.
     *
     * @param U If not null then the results will be stored here.  Otherwise a new matrix will be created.
     * @return The extracted Q matrix.
     */
    public T getU( T U , boolean transpose , boolean compact );


    /**
     * Returns the orthogonal V matrix.
     *
     * @param V If not null then the results will be stored here.  Otherwise a new matrix will be created.
     * @return The extracted Q matrix.
     */
    public T getV( T V ,  boolean transpose , boolean compact );

    /**
     * Extracts the diagonal and off diagonal elements from the decomposition.
     *
     * @param diag diagonal elements from B.
     * @param off off diagonal elements form B.
     */
    public void getDiagonal( double diag[], double off[] );

}