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Java example source code file (ConstantVoltageExample.java)

This example Java source code file (ConstantVoltageExample.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arial, array2drowrealmatrix, arraylist, awt, chart, display, font, gui, iteration, jcomponent, kalmanfilter, list, realmatrix, swing, util, voltage, voltmeter

The ConstantVoltageExample.java Java example source code

/*
 * 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.userguide.filter;

import java.awt.Color;
import java.awt.Component;
import java.awt.Font;
import java.util.ArrayList;
import java.util.List;

import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JComponent;
import javax.swing.JPanel;

import org.apache.commons.math3.filter.DefaultMeasurementModel;
import org.apache.commons.math3.filter.DefaultProcessModel;
import org.apache.commons.math3.filter.KalmanFilter;
import org.apache.commons.math3.filter.MeasurementModel;
import org.apache.commons.math3.filter.ProcessModel;
import org.apache.commons.math3.linear.Array2DRowRealMatrix;
import org.apache.commons.math3.linear.ArrayRealVector;
import org.apache.commons.math3.linear.RealMatrix;
import org.apache.commons.math3.linear.RealVector;
import org.apache.commons.math3.random.RandomGenerator;
import org.apache.commons.math3.random.Well19937c;
import org.apache.commons.math3.userguide.ExampleUtils;
import org.apache.commons.math3.userguide.ExampleUtils.ExampleFrame;

import com.xeiam.xchart.Chart;
import com.xeiam.xchart.ChartBuilder;
import com.xeiam.xchart.Series;
import com.xeiam.xchart.SeriesLineStyle;
import com.xeiam.xchart.SeriesMarker;
import com.xeiam.xchart.XChartPanel;
import com.xeiam.xchart.StyleManager.ChartType;
import com.xeiam.xchart.StyleManager.LegendPosition;

public class ConstantVoltageExample {

    public static class VoltMeter {
        
        private final double initialVoltage;
        private final double processNoise;
        private final double measurementNoise;
        private final RandomGenerator rng;

        private double voltage;

        public VoltMeter(double voltage, double processNoise, double measurementNoise, int seed) {
            this.initialVoltage = voltage;
            this.voltage = voltage;
            this.processNoise = processNoise;
            this.measurementNoise = measurementNoise;
            rng = new Well19937c(seed);
        }
        
        /**
         * Returns the real voltage without any measurement noise.
         *  
         * @return the real voltage
         */
        public double getVoltage() {
            return voltage;
        }
        
        public double getMeasuredVoltage() {
            return getVoltage() + rng.nextGaussian() * measurementNoise; 
        }
        
        public void step() {
            // we apply only the process noise
            voltage = initialVoltage + rng.nextGaussian() * processNoise;
        }
    }

    /** constant voltage test */
    public static void constantVoltageTest(Chart chart1, Chart chart2) {

        final double voltage = 1.25d;
        final double measurementNoise = 0.2d; // measurement noise (V) - std dev
        final double processNoise = 1e-5d;

        final VoltMeter voltMeter = new VoltMeter(voltage, processNoise, measurementNoise, 2);
        
        // the state transition matrix -> constant
        final RealMatrix A = new Array2DRowRealMatrix(new double[] { 1d });

        // the control matrix -> no control input
        final RealMatrix B = new Array2DRowRealMatrix(new double[] { 0d });

        // the measurement matrix -> we measure the voltage directly
        final RealMatrix H = new Array2DRowRealMatrix(new double[] { 1d });

        // the initial state vector -> slightly wrong
        final RealVector x0 = new ArrayRealVector(new double[] { 1.45 });
        
        // the process covariance matrix
        final RealMatrix Q = new Array2DRowRealMatrix(new double[] { processNoise * processNoise });

        // the initial error covariance -> assume a large error at the beginning
        final RealMatrix P0 = new Array2DRowRealMatrix(new double[] { 0.1 });

        // the measurement covariance matrix -> put the "real" variance
        RealMatrix R = new Array2DRowRealMatrix(new double[] { measurementNoise * measurementNoise });

        final ProcessModel pm = new DefaultProcessModel(A, B, Q, x0, P0);
        final MeasurementModel mm = new DefaultMeasurementModel(H, R);
        final KalmanFilter filter = new KalmanFilter(pm, mm);

        final List<Number> xAxis = new ArrayList();
        final List<Number> realVoltageSeries = new ArrayList();
        final List<Number> measuredVoltageSeries = new ArrayList();
        final List<Number> kalmanVoltageSeries = new ArrayList();

        final List<Number> covSeries = new ArrayList();
        
        for (int i = 0; i < 300; i++) {
            xAxis.add(i);

            voltMeter.step();

            realVoltageSeries.add(voltMeter.getVoltage());

            // get the measured voltage from the volt meter
            final double measuredVoltage = voltMeter.getMeasuredVoltage();
            measuredVoltageSeries.add(measuredVoltage);

            kalmanVoltageSeries.add(filter.getStateEstimation()[0]);
            covSeries.add(filter.getErrorCovariance()[0][0]);

            filter.predict();
            filter.correct(new double[] { measuredVoltage });
        }

        chart1.setYAxisTitle("Voltage");
        chart1.setXAxisTitle("Iteration");

        Series dataset = chart1.addSeries("real", xAxis, realVoltageSeries);
        dataset.setMarker(SeriesMarker.NONE);
        
        dataset = chart1.addSeries("measured", xAxis, measuredVoltageSeries);
        dataset.setLineStyle(SeriesLineStyle.DOT_DOT);
        dataset.setMarker(SeriesMarker.NONE);

        dataset = chart1.addSeries("filtered", xAxis, kalmanVoltageSeries);
        dataset.setLineColor(Color.red);
        dataset.setLineStyle(SeriesLineStyle.DASH_DASH);
        dataset.setMarker(SeriesMarker.NONE);

        // Error covariance chart

        chart2.setYAxisTitle("(Voltage)²");
        chart2.setXAxisTitle("Iteration");
        
        dataset = chart2.addSeries("cov", xAxis, covSeries);
        dataset.setLineColor(Color.black);
        dataset.setLineStyle(SeriesLineStyle.SOLID);
        dataset.setMarker(SeriesMarker.NONE);

    }

    public static Chart createChart(String title, int width, int height,
                                    LegendPosition position, boolean legendVisible) {
        Chart chart = new ChartBuilder().width(width).height(height).build();

        // Customize Chart
        chart.setChartTitle(title);
        chart.getStyleManager().setChartTitleVisible(true);
        chart.getStyleManager().setChartTitleFont(new Font("Arial", Font.PLAIN, 12));
        chart.getStyleManager().setLegendPosition(position);
        chart.getStyleManager().setLegendVisible(legendVisible);
        chart.getStyleManager().setLegendFont(new Font("Arial", Font.PLAIN, 12));
        chart.getStyleManager().setLegendPadding(6);
        chart.getStyleManager().setLegendSeriesLineLength(10);
        chart.getStyleManager().setAxisTickLabelsFont(new Font("Arial", Font.PLAIN, 10));
        
        chart.getStyleManager().setChartBackgroundColor(Color.white);
        chart.getStyleManager().setChartPadding(4);
        
        chart.getStyleManager().setChartType(ChartType.Line);
        return chart;
    }

    public static JComponent createComponent() {
        JComponent container = new JPanel();
        container.setLayout(new BoxLayout(container, BoxLayout.LINE_AXIS));
        
        Chart chart1 = createChart("Voltage", 550, 450, LegendPosition.InsideNE, true);
        Chart chart2 = createChart("Error Covariance", 450, 450, LegendPosition.InsideNE, false);
        
        constantVoltageTest(chart1, chart2);

        container.add(new XChartPanel(chart1));
        container.add(new XChartPanel(chart2));
        
        container.setBorder(BorderFactory.createLineBorder(Color.black, 1));
        return container;
    }

    @SuppressWarnings("serial")
    public static class Display extends ExampleFrame {
        
        private JComponent container;

        public Display() {
            setTitle("Commons-Math: Kalman Filter example");
            setSize(1100, 700);
            
            container = new JPanel();

            JComponent comp = createComponent();
            container.add(comp);

            add(container);
        }

        @Override
        public Component getMainPanel() {
            return container;
        }
    }

    public static void main(String[] args) {
        ExampleUtils.showExampleFrame(new Display());
    }

}

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