QQPlot.java

/*
 * Class:        QQPlot
 * Description:  qq-plot
 * Environment:  Java
 * Software:     SSJ 
 * Copyright (C) 2001  Pierre L'Ecuyer and Universite de Montreal
 * Organization: DIRO, Universite de Montreal
 * @author       Richard Simard
 * @since        May 2011
 *
 *
 * Licensed 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 umontreal.ssj.charts;
 
import umontreal.ssj.probdist.ContinuousDistribution;
import java.util.Arrays;

public class QQPlot extends XYLineChart {
   private double[][] Q; // data points
   private double[][] Lin; // line y = x
 
   private void initLinear(double a, double b) {
      // line y = x in [a, b] by steps of h
      int m = 100;
      double h = (b - a) / m;
      Lin = new double[2][m + 1];
      for (int i = 0; i <= m; i++)
         Lin[0][i] = Lin[1][i] = a + h * i;
   }
 
   private void initPoints(ContinuousDistribution dist, double[] data, int numPoints) {
      int i;
      double p;
      Q = new double[2][numPoints]; // q_i = cdf^(-1)(p_i)
 
      for (i = 0; i < numPoints; i++)
         Q[1][i] = data[i];
      Arrays.sort(Q[1]);
      for (i = 0; i < numPoints; i++) {
         p = (i + 0.5) / numPoints;
         Q[0][i] = dist.inverseF(p);
      }
   }

   public QQPlot(String title, String XLabel, String YLabel, ContinuousDistribution dist, double[] X) {
      this(title, XLabel, YLabel, dist, X, X.length);
   }

   public QQPlot(String title, String XLabel, String YLabel, ContinuousDistribution dist, double[] X, int numPoints) {
      super();
      initPoints(dist, X, numPoints);
      initLinear(Q[1][0], Q[1][numPoints - 1]);
      dataset = new XYListSeriesCollection(Q, Lin);
      // --- dashed line for y = x
      ((XYListSeriesCollection) dataset).setDashPattern(1, "dashed");
      init(title, XLabel, YLabel);
   }

   public QQPlot(String title, String XLabel, String YLabel, ContinuousDistribution dist, double[][] data, int r) {
      this(title, XLabel, YLabel, dist, data[r], data[r].length);
   }
}