1/*2* Licensed to the Apache Software Foundation (ASF) under one or more3* contributor license agreements. See the NOTICE file distributed with4* this work for additional information regarding copyright ownership.5* The ASF licenses this file to You under the Apache License, Version 2.06* (the "License"); you may not use this file except in compliance with7* the License. You may obtain a copy of the License at8*9* http://www.apache.org/licenses/LICENSE-2.010*11* Unless required by applicable law or agreed to in writing, software12* 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 and15* limitations under the License.16*/17 18packageorg.apache.commons.math3.optimization.general; 19 20/**21* This interface represents a preconditioner for differentiable scalar22* objective function optimizers.23* @deprecated As of 3.1 (to be removed in 4.0).24* @since 2.025*/26 @Deprecated 27publicinterfacePreconditioner { 28/**29* Precondition a search direction.30* <p>31* The returned preconditioned search direction must be computed fast or32* the algorithm performances will drop drastically. A classical approach33* is to compute only the diagonal elements of the hessian and to divide34* the raw search direction by these elements if they are all positive.35* If at least one of them is negative, it is safer to return a clone of36* the raw search direction as if the hessian was the identity matrix. The37* rationale for this simplified choice is that a negative diagonal element38* means the current point is far from the optimum and preconditioning will39* not be efficient anyway in this case.40* </p>41* @param point current point at which the search direction was computed42* @param r raw search direction (i.e. opposite of the gradient)43* @return approximation of H<sup>-1</sup>r where H is the objective function hessian44*/45double[] precondition(double[] point,double[] r); 46 }