| // 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.spaceroots.mantissa.quadrature.scalar; |
| |
| import org.spaceroots.mantissa.functions.scalar.*; |
| import org.spaceroots.mantissa.functions.FunctionException; |
| import org.spaceroots.mantissa.functions.ExhaustedSampleException; |
| |
| /** This class implements an enhanced Simpson integrator as a sample. |
| |
| * <p>A traditional Simpson integrator is based on a quadratic |
| * approximation of the function on three equally spaced points. This |
| * integrator does the same thing but can handle non-equally spaced |
| * points. If it is used on a regular sample, it behaves exactly as a |
| * traditional Simpson integrator.</p> |
| |
| * @see EnhancedSimpsonIntegrator |
| |
| * @version $Id$ |
| * @author L. Maisonobe |
| |
| */ |
| |
| public class EnhancedSimpsonIntegratorSampler |
| implements SampledFunctionIterator { |
| |
| /** Underlying sampled function iterator. */ |
| private SampledFunctionIterator iter; |
| |
| /** Next point. */ |
| private ScalarValuedPair next; |
| |
| /** Current running sum. */ |
| private double sum; |
| |
| /** Constructor. |
| * Build an integrator from an underlying sample iterator. |
| * @param iter iterator over the base function |
| */ |
| public EnhancedSimpsonIntegratorSampler(SampledFunctionIterator iter) |
| throws ExhaustedSampleException, FunctionException { |
| |
| this.iter = iter; |
| |
| // get the first point |
| next = iter.nextSamplePoint(); |
| |
| // initialize the sum |
| sum = 0.0; |
| |
| } |
| |
| public boolean hasNext() { |
| return iter.hasNext(); |
| } |
| |
| public ScalarValuedPair nextSamplePoint() |
| throws ExhaustedSampleException, FunctionException { |
| // performs one step of an enhanced Simpson scheme |
| ScalarValuedPair previous = next; |
| ScalarValuedPair current = iter.nextSamplePoint(); |
| |
| try { |
| next = iter.nextSamplePoint(); |
| |
| double h1 = current.getX() - previous.getX(); |
| double h2 = next.getX() - current.getX(); |
| double cP = (h1 + h2) * (2 * h1 - h2) / (6 * h1); |
| double cC = (h1 + h2) * (h1 + h2) * (h1 + h2) / (6 * h1 * h2); |
| double cN = (h1 + h2) * (2 * h2 - h1) / (6 * h2); |
| |
| sum += cP * previous.getY() + cC * current.getY() + cN * next.getY(); |
| |
| } catch(ExhaustedSampleException e) { |
| // we have an incomplete step at the end of the sample |
| // we use a trapezoid scheme for this last step |
| sum += 0.5 * (current.getX() - previous.getX()) * (previous.getY() + current.getY()); |
| return new ScalarValuedPair(current.getX(), sum); |
| } |
| |
| return new ScalarValuedPair(next.getX(), sum); |
| |
| } |
| |
| } |