Raymond | dee0849 | 2015-04-02 10:43:13 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Licensed to the Apache Software Foundation (ASF) under one or more |
| 3 | * contributor license agreements. See the NOTICE file distributed with |
| 4 | * this work for additional information regarding copyright ownership. |
| 5 | * The ASF licenses this file to You under the Apache License, Version 2.0 |
| 6 | * (the "License"); you may not use this file except in compliance with |
| 7 | * the License. You may obtain a copy of the License at |
| 8 | * |
| 9 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 10 | * |
| 11 | * Unless required by applicable law or agreed to in writing, software |
| 12 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 13 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 14 | * See the License for the specific language governing permissions and |
| 15 | * limitations under the License. |
| 16 | */ |
| 17 | |
| 18 | package org.apache.commons.math.optimization.general; |
| 19 | |
| 20 | import org.apache.commons.math.FunctionEvaluationException; |
| 21 | |
| 22 | /** |
| 23 | * This interface represents a preconditioner for differentiable scalar |
| 24 | * objective function optimizers. |
| 25 | * @version $Revision: 1073158 $ $Date: 2011-02-21 22:46:52 +0100 (lun. 21 févr. 2011) $ |
| 26 | * @since 2.0 |
| 27 | */ |
| 28 | public interface Preconditioner { |
| 29 | |
| 30 | /** |
| 31 | * Precondition a search direction. |
| 32 | * <p> |
| 33 | * The returned preconditioned search direction must be computed fast or |
| 34 | * the algorithm performances will drop drastically. A classical approach |
| 35 | * is to compute only the diagonal elements of the hessian and to divide |
| 36 | * the raw search direction by these elements if they are all positive. |
| 37 | * If at least one of them is negative, it is safer to return a clone of |
| 38 | * the raw search direction as if the hessian was the identity matrix. The |
| 39 | * rationale for this simplified choice is that a negative diagonal element |
| 40 | * means the current point is far from the optimum and preconditioning will |
| 41 | * not be efficient anyway in this case. |
| 42 | * </p> |
| 43 | * @param point current point at which the search direction was computed |
| 44 | * @param r raw search direction (i.e. opposite of the gradient) |
| 45 | * @return approximation of H<sup>-1</sup>r where H is the objective function hessian |
| 46 | * @exception FunctionEvaluationException if no cost can be computed for the parameters |
| 47 | * @exception IllegalArgumentException if point dimension is wrong |
| 48 | */ |
| 49 | double[] precondition(double[] point, double[] r) |
| 50 | throws FunctionEvaluationException, IllegalArgumentException; |
| 51 | |
| 52 | } |