    001    /*
    002     * Licensed to the Apache Software Foundation (ASF) under one or more
    003     * contributor license agreements.  See the NOTICE file distributed with
    004     * this work for additional information regarding copyright ownership.
    005     * The ASF licenses this file to You under the Apache License, Version 2.0
    006     * (the "License"); you may not use this file except in compliance with
    007     * the License.  You may obtain a copy of the License at
    008     *
    009     *      http://www.apache.org/licenses/LICENSE-2.0
    010     *
    011     * Unless required by applicable law or agreed to in writing, software
    012     * distributed under the License is distributed on an "AS IS" BASIS,
    013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014     * See the License for the specific language governing permissions and
    015     * limitations under the License.
    016     */
    017
    018    package org.apache.commons.math3.linear;
    019
    020
    021
    022    /**
    023     * Interface handling decomposition algorithms that can solve A &times; X = B.
    024     * <p>Decomposition algorithms decompose an A matrix has a product of several specific
    025     * matrices from which they can solve A &times; X = B in least squares sense: they find X
    026     * such that ||A &times; X - B|| is minimal.</p>
    027     * <p>Some solvers like {@link LUDecomposition} can only find the solution for
    028     * square matrices and when the solution is an exact linear solution, i.e. when
    029     * ||A &times; X - B|| is exactly 0. Other solvers can also find solutions
    030     * with non-square matrix A and with non-null minimal norm. If an exact linear
    031     * solution exists it is also the minimal norm solution.</p>
    032     *
    033     * @version $Id: DecompositionSolver.java 1416643 2012-12-03 19:37:14Z tn $
    034     * @since 2.0
    035     */
    036    public interface DecompositionSolver {
    037
    038        /** Solve the linear equation A &times; X = B for matrices A.
    039         * <p>The A matrix is implicit, it is provided by the underlying
    040         * decomposition algorithm.</p>
    041         * @param b right-hand side of the equation A &times; X = B
    042         * @return a vector X that minimizes the two norm of A &times; X - B
    043         * @throws org.apache.commons.math3.exception.DimensionMismatchException
    044         * if the matrices dimensions do not match.
    045         * @throws SingularMatrixException
    046         * if the decomposed matrix is singular.
    047         */
    048        RealVector solve(final RealVector b);
    049
    050        /** Solve the linear equation A &times; X = B for matrices A.
    051         * <p>The A matrix is implicit, it is provided by the underlying
    052         * decomposition algorithm.</p>
    053         * @param b right-hand side of the equation A &times; X = B
    054         * @return a matrix X that minimizes the two norm of A &times; X - B
    055         * @throws org.apache.commons.math3.exception.DimensionMismatchException
    056         * if the matrices dimensions do not match.
    057         * @throws SingularMatrixException
    058         * if the decomposed matrix is singular.
    059         */
    060        RealMatrix solve(final RealMatrix b);
    061
    062        /**
    063         * Check if the decomposed matrix is non-singular.
    064         * @return true if the decomposed matrix is non-singular.
    065         */
    066        boolean isNonSingular();
    067
    068        /** Get the inverse (or pseudo-inverse) of the decomposed matrix.
    069         * @return inverse matrix
    070         * @throws SingularMatrixException
    071         * if the decomposed matrix is singular.
    072         */
    073        RealMatrix getInverse();
    074    }