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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.math3.linear;
import org.apache.commons.math3.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.
*
* <p>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>
* <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
* </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.math3.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;
}
}
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