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      1 /*
      2  * Licensed to the Apache Software Foundation (ASF) under one or more
      3  * contributor license agreements.  See the NOTICE file distributed with
      4  * this work for additional information regarding copyright ownership.
      5  * The ASF licenses this file to You under the Apache License, Version 2.0
      6  * (the "License"); you may not use this file except in compliance with
      7  * the License.  You may obtain a copy of the License at
      8  *
      9  *      http://www.apache.org/licenses/LICENSE-2.0
     10  *
     11  * Unless required by applicable law or agreed to in writing, software
     12  * distributed under the License is distributed on an "AS IS" BASIS,
     13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     14  * See the License for the specific language governing permissions and
     15  * limitations under the License.
     16  */
     17 
     18 package org.apache.commons.math.linear;
     19 
     20 
     21 /**
     22  * An interface to classes that implement an algorithm to calculate the
     23  * QR-decomposition of a real matrix.
     24  * <p>This interface is based on the class with similar name from the
     25  * <a href="http://math.nist.gov/javanumerics/jama/">JAMA</a> library, with the
     26  * following changes:</p>
     27  * <ul>
     28  *   <li>a {@link #getQT() getQT} method has been added,</li>
     29  *   <li>the <code>solve</code> and <code>isFullRank</code> methods have been replaced
     30  *   by a {@link #getSolver() getSolver} method and the equivalent methods provided by
     31  *   the returned {@link DecompositionSolver}.</li>
     32  * </ul>
     33  *
     34  * @see <a href="http://mathworld.wolfram.com/QRDecomposition.html">MathWorld</a>
     35  * @see <a href="http://en.wikipedia.org/wiki/QR_decomposition">Wikipedia</a>
     36  * @version $Revision: 826627 $ $Date: 2009-10-19 12:27:47 +0200 (lun. 19 oct. 2009) $
     37  * @since 1.2
     38  */
     39 public interface QRDecomposition {
     40 
     41     /**
     42      * Returns the matrix R of the decomposition.
     43      * <p>R is an upper-triangular matrix</p>
     44      * @return the R matrix
     45      */
     46     RealMatrix getR();
     47 
     48     /**
     49      * Returns the matrix Q of the decomposition.
     50      * <p>Q is an orthogonal matrix</p>
     51      * @return the Q matrix
     52      */
     53     RealMatrix getQ();
     54 
     55     /**
     56      * Returns the transpose of the matrix Q of the decomposition.
     57      * <p>Q is an orthogonal matrix</p>
     58      * @return the Q matrix
     59      */
     60     RealMatrix getQT();
     61 
     62     /**
     63      * Returns the Householder reflector vectors.
     64      * <p>H is a lower trapezoidal matrix whose columns represent
     65      * each successive Householder reflector vector. This matrix is used
     66      * to compute Q.</p>
     67      * @return a matrix containing the Householder reflector vectors
     68      */
     69     RealMatrix getH();
     70 
     71     /**
     72      * Get a solver for finding the A &times; X = B solution in least square sense.
     73      * @return a solver
     74      */
     75     DecompositionSolver getSolver();
     76 
     77 }
     78