package net.sf.openrocket.util;
-import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
-import java.util.Map;
+import java.util.SortedMap;
import java.util.TreeMap;
public class LinearInterpolator implements Cloneable {
*/
public LinearInterpolator() {
}
-
+
/**
* Construct a <code>LinearInterpolator</code> with the given points.
*
public LinearInterpolator(double[] x, double[] y) {
addPoints(x,y);
}
-
+
public LinearInterpolator(List<Double> x, List<Double> y) {
addPoints(x,y);
}
-
+
/**
* Add the point to the linear interpolation.
*
public void addPoint(double x, double y) {
sortMap.put(x, y);
}
-
+
/**
* Add the points to the linear interpolation.
*
sortMap.put(x[i],y[i]);
}
}
-
+
public void addPoints(List<Double> x, List<Double> y){
if (x.size() != y.size()) {
throw new IllegalArgumentException("Array lengths do not match, x="+x.size() +
sortMap.put( (Double) x.toArray()[i], (Double) y.toArray()[i]);
}
}
-
-
+
+
public double getValue(double x) {
- Map.Entry<Double,Double> e1, e2;
double x1, x2;
- double y1, y2;
+ Double y1, y2;
+ // Froyo does not support floorEntry, firstEntry or higherEntry. We instead have to
+ // resort to using other more awkward methods.
+
+ y1 = sortMap.get(x);
+
+ if ( y1 != null ) {
+ // Wow, x was a key in the map. Such luck.
+ return y1.doubleValue();
+ }
+
+ // we now know that x is not in the map, so we need to find the lower and higher keys.
- e1 = sortMap.floorEntry(x);
+ // let's just make certain that our map is not empty.
+ if ( sortMap.isEmpty() ) {
+ throw new IllegalStateException("No points added yet to the interpolator.");
+ }
- if (e1 == null) {
- // x smaller than any value in the set
- e1 = sortMap.firstEntry();
- if (e1 == null) {
- throw new IllegalStateException("No points added yet to the interpolator.");
- }
- return e1.getValue();
+ // firstKey in the map - cannot be null since the map is not empty.
+ Double firstKey = sortMap.firstKey();
+
+ // x is smaller than the first entry in the map.
+ if ( x < firstKey.doubleValue() ) {
+ y1 = sortMap.get(firstKey);
+ return y1.doubleValue();
}
- x1 = e1.getKey();
- e2 = sortMap.higherEntry(x1);
+ // floor key is the largest key smaller than x - since we have at least one key,
+ // and x>=firstKey, we know that floorKey != null.
+ Double floorKey = sortMap.subMap(firstKey, x).lastKey();
+
+ x1 = floorKey.doubleValue();
+ y1 = sortMap.get(floorKey);
- if (e2 == null) {
- // x larger than any value in the set
- return e1.getValue();
+ // Now we need to find the key that is greater or equal to x
+ SortedMap<Double,Double> tailMap = sortMap.tailMap(x);
+
+ // Check if x is bigger than all the entries.
+ if ( tailMap.isEmpty() ) {
+ return y1.doubleValue();
}
+ Double ceilKey = tailMap.firstKey();
- x2 = e2.getKey();
- y1 = e1.getValue();
- y2 = e2.getValue();
+ // Check if x is bigger than all the entries.
+ if ( ceilKey == null ) {
+ return y1.doubleValue();
+ }
+ x2 = ceilKey.doubleValue();
+ y2 = sortMap.get(ceilKey);
+
return (x - x1)/(x2-x1) * (y2-y1) + y1;
}
-
-
+
+
public double[] getXPoints() {
double[] x = new double[sortMap.size()];
Iterator<Double> iter = sortMap.keySet().iterator();
}
return x;
}
-
-
+
+
@SuppressWarnings("unchecked")
@Override
public LinearInterpolator clone() {
}
}
-
- public static void main(String[] args) {
- LinearInterpolator interpolator = new LinearInterpolator(
- new double[] {1, 1.5, 2, 4, 5},
- new double[] {0, 1, 0, 2, 2}
- );
-
- for (double x=0; x < 6; x+=0.1) {
- System.out.printf("%.1f: %.2f\n", x, interpolator.getValue(x));
- }
-
- // Should be the same
-
- ArrayList<Double> time = new ArrayList<Double>( Arrays.asList( new Double[] {1.0, 1.5, 2.0, 4.0, 5.0} ));
- ArrayList<Double> y = new ArrayList<Double>( Arrays.asList( new Double[] {0.0, 1.0, 0.0, 2.0, 2.0} ));
-
- LinearInterpolator interpolator2 = new LinearInterpolator(time,y);
- for (double x=0; x < 6; x+=0.1) {
- System.out.printf("%.1f: %.2f\n", x, interpolator2.getValue(x));
- }
- }
}