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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.math.optimization;
+
+/** This interface specifies how to check if a {@link
+ * DifferentiableMultivariateVectorialOptimizer optimization algorithm} has converged.
+ *
+ * <p>Deciding if convergence has been reached is a problem-dependent issue. The
+ * user should provide a class implementing this interface to allow the optimization
+ * algorithm to stop its search according to the problem at hand.</p>
+ * <p>For convenience, two implementations that fit simple needs are already provided:
+ * {@link SimpleVectorialValueChecker} and {@link SimpleVectorialPointChecker}. The first
+ * one considers convergence is reached when the objective function value does not
+ * change much anymore, it does not use the point set at all. The second one
+ * considers convergence is reached when the input point set does not change
+ * much anymore, it does not use objective function value at all.</p>
+ *
+ * @version $Revision: 780674 $ $Date: 2009-06-01 17:10:55 +0200 (lun. 01 juin 2009) $
+ * @since 2.0
+ */
+
+public interface VectorialConvergenceChecker {
+
+  /** Check if the optimization algorithm has converged considering the last points.
+   * <p>
+   * This method may be called several time from the same algorithm iteration with
+   * different points. This can be detected by checking the iteration number at each
+   * call if needed. Each time this method is called, the previous and current point
+   * correspond to points with the same role at each iteration, so they can be
+   * compared. As an example, simplex-based algorithms call this method for all
+   * points of the simplex, not only for the best or worst ones.
+   * </p>
+   * @param iteration index of current iteration
+   * @param previous point from previous iteration
+   * @param current point from current iteration
+   * @return true if the algorithm is considered to have converged
+   */
+  boolean converged(int iteration, VectorialPointValuePair previous, VectorialPointValuePair current);
+
+}