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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.optim.univariate;
+
+import org.apache.commons.math3.util.FastMath;
+import org.apache.commons.math3.exception.NotStrictlyPositiveException;
+import org.apache.commons.math3.optim.AbstractConvergenceChecker;
+
+/**
+ * Simple implementation of the
+ * {@link org.apache.commons.math3.optimization.ConvergenceChecker} interface
+ * that uses only objective function values.
+ *
+ * Convergence is considered to have been reached if either the relative
+ * difference between the objective function values is smaller than a
+ * threshold or if either the absolute difference between the objective
+ * function values is smaller than another threshold.
+ * <br/>
+ * The {@link #converged(int,UnivariatePointValuePair,UnivariatePointValuePair)
+ * converged} method will also return {@code true} if the number of iterations
+ * has been set (see {@link #SimpleUnivariateValueChecker(double,double,int)
+ * this constructor}).
+ *
+ * @since 3.1
+ */
+public class SimpleUnivariateValueChecker
+ extends AbstractConvergenceChecker<UnivariatePointValuePair> {
+ /**
+ * If {@link #maxIterationCount} is set to this value, the number of
+ * iterations will never cause
+ * {@link #converged(int,UnivariatePointValuePair,UnivariatePointValuePair)}
+ * to return {@code true}.
+ */
+ private static final int ITERATION_CHECK_DISABLED = -1;
+ /**
+ * Number of iterations after which the
+ * {@link #converged(int,UnivariatePointValuePair,UnivariatePointValuePair)}
+ * method will return true (unless the check is disabled).
+ */
+ private final int maxIterationCount;
+
+ /** Build an instance with specified thresholds.
+ *
+ * In order to perform only relative checks, the absolute tolerance
+ * must be set to a negative value. In order to perform only absolute
+ * checks, the relative tolerance must be set to a negative value.
+ *
+ * @param relativeThreshold relative tolerance threshold
+ * @param absoluteThreshold absolute tolerance threshold
+ */
+ public SimpleUnivariateValueChecker(final double relativeThreshold,
+ final double absoluteThreshold) {
+ super(relativeThreshold, absoluteThreshold);
+ maxIterationCount = ITERATION_CHECK_DISABLED;
+ }
+
+ /**
+ * Builds an instance with specified thresholds.
+ *
+ * In order to perform only relative checks, the absolute tolerance
+ * must be set to a negative value. In order to perform only absolute
+ * checks, the relative tolerance must be set to a negative value.
+ *
+ * @param relativeThreshold relative tolerance threshold
+ * @param absoluteThreshold absolute tolerance threshold
+ * @param maxIter Maximum iteration count.
+ * @throws NotStrictlyPositiveException if {@code maxIter <= 0}.
+ *
+ * @since 3.1
+ */
+ public SimpleUnivariateValueChecker(final double relativeThreshold,
+ final double absoluteThreshold,
+ final int maxIter) {
+ super(relativeThreshold, absoluteThreshold);
+
+ if (maxIter <= 0) {
+ throw new NotStrictlyPositiveException(maxIter);
+ }
+ maxIterationCount = maxIter;
+ }
+
+ /**
+ * Check if the optimization algorithm has converged considering the
+ * last two points.
+ * 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.
+ *
+ * @param iteration Index of current iteration
+ * @param previous Best point in the previous iteration.
+ * @param current Best point in the current iteration.
+ * @return {@code true} if the algorithm has converged.
+ */
+ @Override
+ public boolean converged(final int iteration,
+ final UnivariatePointValuePair previous,
+ final UnivariatePointValuePair current) {
+ if (maxIterationCount != ITERATION_CHECK_DISABLED && iteration >= maxIterationCount) {
+ return true;
+ }
+
+ final double p = previous.getValue();
+ final double c = current.getValue();
+ final double difference = FastMath.abs(p - c);
+ final double size = FastMath.max(FastMath.abs(p), FastMath.abs(c));
+ return difference <= size * getRelativeThreshold() ||
+ difference <= getAbsoluteThreshold();
+ }
+}