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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
+ * LU-decomposition of a real matrix.
+ * <p>The LU-decomposition of matrix A is a set of three matrices: P, L and U
+ * such that P&times;A = L&times;U. P is a rows permutation matrix that is used
+ * to rearrange the rows of A before so that it can be decomposed. L is a lower
+ * triangular matrix with unit diagonal terms and U is an upper triangular matrix.</p>
+ * <p>This interface is based on the class with similar name from the
+ * <a href="http://math.nist.gov/javanumerics/jama/">JAMA</a> library.</p>
+ * <ul>
+ *   <li>a {@link #getP() getP} method has been added,</li>
+ *   <li>the <code>det</code> method has been renamed as {@link #getDeterminant()
+ *   getDeterminant},</li>
+ *   <li>the <code>getDoublePivot</code> method has been removed (but the int based
+ *   {@link #getPivot() getPivot} method has been kept),</li>
+ *   <li>the <code>solve</code> and <code>isNonSingular</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/LUDecomposition.html">MathWorld</a>
+ * @see <a href="http://en.wikipedia.org/wiki/LU_decomposition">Wikipedia</a>
+ * @version $Revision: 826627 $ $Date: 2009-10-19 12:27:47 +0200 (lun. 19 oct. 2009) $
+ * @since 2.0
+ */
+public interface LUDecomposition {
+
+    /**
+     * Returns the matrix L of the decomposition.
+     * <p>L is an lower-triangular matrix</p>
+     * @return the L matrix (or null if decomposed matrix is singular)
+     */
+    RealMatrix getL();
+
+    /**
+     * Returns the matrix U of the decomposition.
+     * <p>U is an upper-triangular matrix</p>
+     * @return the U matrix (or null if decomposed matrix is singular)
+     */
+    RealMatrix getU();
+
+    /**
+     * Returns the P rows permutation matrix.
+     * <p>P is a sparse matrix with exactly one element set to 1.0 in
+     * each row and each column, all other elements being set to 0.0.</p>
+     * <p>The positions of the 1 elements are given by the {@link #getPivot()
+     * pivot permutation vector}.</p>
+     * @return the P rows permutation matrix (or null if decomposed matrix is singular)
+     * @see #getPivot()
+     */
+    RealMatrix getP();
+
+    /**
+     * Returns the pivot permutation vector.
+     * @return the pivot permutation vector
+     * @see #getP()
+     */
+    int[] getPivot();
+
+    /**
+     * Return the determinant of the matrix
+     * @return determinant of the matrix
+     */
+    double getDeterminant();
+
+    /**
+     * Get a solver for finding the A &times; X = B solution in exact linear sense.
+     * @return a solver
+     */
+    DecompositionSolver getSolver();
+
+}