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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.commons.math.linear;
+
+
+/**
+ * An interface to classes that implement an algorithm to calculate the
+ * QR-decomposition of a real matrix.
+ * <p>This interface is based on the class with similar name from the
+ * <a href="http://math.nist.gov/javanumerics/jama/">JAMA</a> library, with the
+ * following changes:</p>
+ * <ul>
+ *   <li>a {@link #getQT() getQT} method has been added,</li>
+ *   <li>the <code>solve</code> and <code>isFullRank</code> methods have been replaced
+ *   by a {@link #getSolver() getSolver} method and the equivalent methods provided by
+ *   the returned {@link DecompositionSolver}.</li>
+ * </ul>
+ *
+ * @see <a href="http://mathworld.wolfram.com/QRDecomposition.html">MathWorld</a>
+ * @see <a href="http://en.wikipedia.org/wiki/QR_decomposition">Wikipedia</a>
+ * @version $Revision: 826627 $ $Date: 2009-10-19 12:27:47 +0200 (lun. 19 oct. 2009) $
+ * @since 1.2
+ */
+public interface QRDecomposition {
+
+    /**
+     * Returns the matrix R of the decomposition.
+     * <p>R is an upper-triangular matrix</p>
+     * @return the R matrix
+     */
+    RealMatrix getR();
+
+    /**
+     * Returns the matrix Q of the decomposition.
+     * <p>Q is an orthogonal matrix</p>
+     * @return the Q matrix
+     */
+    RealMatrix getQ();
+
+    /**
+     * Returns the transpose of the matrix Q of the decomposition.
+     * <p>Q is an orthogonal matrix</p>
+     * @return the Q matrix
+     */
+    RealMatrix getQT();
+
+    /**
+     * Returns the Householder reflector vectors.
+     * <p>H is a lower trapezoidal matrix whose columns represent
+     * each successive Householder reflector vector. This matrix is used
+     * to compute Q.</p>
+     * @return a matrix containing the Householder reflector vectors
+     */
+    RealMatrix getH();
+
+    /**
+     * Get a solver for finding the A &times; X = B solution in least square sense.
+     * @return a solver
+     */
+    DecompositionSolver getSolver();
+
+}