| /* |
| * 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.math4.linear; |
| |
| import org.apache.commons.math4.exception.DimensionMismatchException; |
| |
| /** |
| * This class defines a linear operator operating on real ({@code double}) |
| * vector spaces. No direct access to the coefficients of the underlying matrix |
| * is provided. |
| * |
| * The motivation for such an interface is well stated by |
| * <a href="#BARR1994">Barrett et al. (1994)</a>: |
| * <blockquote> |
| * We restrict ourselves to iterative methods, which work by repeatedly |
| * improving an approximate solution until it is accurate enough. These |
| * methods access the coefficient matrix A of the linear system only via the |
| * matrix-vector product y = A · x |
| * (and perhaps z = A<sup>T</sup> · x). Thus the user need only |
| * supply a subroutine for computing y (and perhaps z) given x, which permits |
| * full exploitation of the sparsity or other special structure of A. |
| * </blockquote> |
| * <br> |
| * |
| * <dl> |
| * <dt><a name="BARR1994">Barret et al. (1994)</a></dt> |
| * <dd> |
| * R. Barrett, M. Berry, T. F. Chan, J. Demmel, J. M. Donato, J. Dongarra, |
| * V. Eijkhout, R. Pozo, C. Romine and H. Van der Vorst, |
| * <em>Templates for the Solution of Linear Systems: Building Blocks for |
| * Iterative Methods</em>, SIAM |
| * </dd> |
| * </dl> |
| * |
| * @since 3.0 |
| */ |
| public abstract class RealLinearOperator { |
| /** |
| * Returns the dimension of the codomain of this operator. |
| * |
| * @return the number of rows of the underlying matrix |
| */ |
| public abstract int getRowDimension(); |
| |
| /** |
| * Returns the dimension of the domain of this operator. |
| * |
| * @return the number of columns of the underlying matrix |
| */ |
| public abstract int getColumnDimension(); |
| |
| /** |
| * Returns the result of multiplying {@code this} by the vector {@code x}. |
| * |
| * @param x the vector to operate on |
| * @return the product of {@code this} instance with {@code x} |
| * @throws DimensionMismatchException if the column dimension does not match |
| * the size of {@code x} |
| */ |
| public abstract RealVector operate(final RealVector x) |
| throws DimensionMismatchException; |
| |
| /** |
| * Returns the result of multiplying the transpose of {@code this} operator |
| * by the vector {@code x} (optional operation). The default implementation |
| * throws an {@link UnsupportedOperationException}. Users overriding this |
| * method must also override {@link #isTransposable()}. |
| * |
| * @param x the vector to operate on |
| * @return the product of the transpose of {@code this} instance with |
| * {@code x} |
| * @throws org.apache.commons.math4.exception.DimensionMismatchException |
| * if the row dimension does not match the size of {@code x} |
| * @throws UnsupportedOperationException if this operation is not supported |
| * by {@code this} operator |
| */ |
| public RealVector operateTranspose(final RealVector x) |
| throws DimensionMismatchException, UnsupportedOperationException { |
| throw new UnsupportedOperationException(); |
| } |
| |
| /** |
| * Returns {@code true} if this operator supports |
| * {@link #operateTranspose(RealVector)}. If {@code true} is returned, |
| * {@link #operateTranspose(RealVector)} should not throw |
| * {@code UnsupportedOperationException}. The default implementation returns |
| * {@code false}. |
| * |
| * @return {@code false} |
| */ |
| public boolean isTransposable() { |
| return false; |
| } |
| } |