git.gag.com Git - debian/openrocket/blob - core/src/net/sf/openrocket/util/LinearInterpolator.java

   1 package net.sf.openrocket.util;
   2
   3 import java.util.Iterator;
   4 import java.util.Map;
   5 import java.util.TreeMap;
   6
   7 public class LinearInterpolator implements Cloneable {
   8
   9         private TreeMap<Double, Double> sortMap = new TreeMap<Double,Double>();
  10
  11         /**
  12          * Construct a <code>LinearInterpolator</code> with no points.  Some points must be
  13          * added using {@link #addPoints(double[], double[])} before using the interpolator.
  14          */
  15         public LinearInterpolator() {
  16         }
  17
  18         /**
  19          * Construct a <code>LinearInterpolator</code> with the given points.
  20          *
  21          * @param x             the x-coordinates of the points.
  22          * @param y             the y-coordinates of the points.
  23          * @throws IllegalArgumentException             if the lengths of <code>x</code> and <code>y</code>
  24          *                                                                              are not equal.
  25          * @see #addPoints(double[], double[])
  26          */
  27         public LinearInterpolator(double[] x, double[] y) {
  28                 addPoints(x,y);
  29         }
  30
  31
  32         /**
  33          * Add the point to the linear interpolation.
  34          *
  35          * @param x             the x-coordinate of the point.
  36          * @param y             the y-coordinate of the point.
  37          */
  38         public void addPoint(double x, double y) {
  39                 sortMap.put(x, y);
  40         }
  41
  42         /**
  43          * Add the points to the linear interpolation.
  44          *
  45          * @param x             the x-coordinates of the points.
  46          * @param y             the y-coordinates of the points.
  47          * @throws IllegalArgumentException             if the lengths of <code>x</code> and <code>y</code>
  48          *                                                                              are not equal.
  49          */
  50         public void addPoints(double[] x, double[] y) {
  51                 if (x.length != y.length) {
  52                         throw new IllegalArgumentException("Array lengths do not match, x="+x.length +
  53                                         " y="+y.length);
  54                 }
  55                 for (int i=0; i < x.length; i++) {
  56                         sortMap.put(x[i],y[i]);
  57                 }
  58         }
  59
  60
  61
  62         public double getValue(double x) {
  63                 Map.Entry<Double,Double> e1, e2;
  64                 double x1, x2;
  65                 double y1, y2;
  66
  67                 e1 = sortMap.floorEntry(x);
  68
  69                 if (e1 == null) {
  70                         // x smaller than any value in the set
  71                         e1 = sortMap.firstEntry();
  72                         if (e1 == null) {
  73                                 throw new IllegalStateException("No points added yet to the interpolator.");
  74                         }
  75                         return e1.getValue();
  76                 }
  77
  78                 x1 = e1.getKey();
  79                 e2 = sortMap.higherEntry(x1);
  80
  81                 if (e2 == null) {
  82                         // x larger than any value in the set
  83                         return e1.getValue();
  84                 }
  85
  86                 x2 = e2.getKey();
  87                 y1 = e1.getValue();
  88                 y2 = e2.getValue();
  89
  90                 return (x - x1)/(x2-x1) * (y2-y1) + y1;
  91         }
  92
  93
  94         public double[] getXPoints() {
  95                 double[] x = new double[sortMap.size()];
  96                 Iterator<Double> iter = sortMap.keySet().iterator();
  97                 for (int i=0; iter.hasNext(); i++) {
  98                         x[i] = iter.next();
  99                 }
 100                 return x;
 101         }
 102
 103
 104         @SuppressWarnings("unchecked")
 105         @Override
 106         public LinearInterpolator clone() {
 107                 try {
 108                         LinearInterpolator other = (LinearInterpolator)super.clone();
 109                         other.sortMap = (TreeMap<Double,Double>)this.sortMap.clone();
 110                         return other;
 111                 } catch (CloneNotSupportedException e) {
 112                         throw new BugException("CloneNotSupportedException?!",e);
 113                 }
 114         }
 115
 116
 117         public static void main(String[] args) {
 118                 LinearInterpolator interpolator = new LinearInterpolator(
 119                                 new double[] {1, 1.5, 2, 4, 5},
 120                                 new double[] {0, 1,   0, 2, 2}
 121                 );
 122
 123                 for (double x=0; x < 6; x+=0.1) {
 124                         System.out.printf("%.1f:  %.2f\n", x, interpolator.getValue(x));
 125                 }
 126         }
 127
 128 }