PR: 34230

Fixed bug in PolynomialSplineFunction to allow evaluation of the function at the last knot point.

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/math/trunk@159727 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/commons/math/analysis/PolynomialSplineFunction.java

@@ -36,7 +36,7 @@ import org.apache.commons.math.FunctionEvaluationException;
  * centered on the knot points to compute the spline function values.  See below.
  * <p>
  * The domain of the polynomial spline function is 
- * <code>[smallest knot, largest knot)</code>.  Attempts to evaluate the
+ * <code>[smallest knot, largest knot]</code>.  Attempts to evaluate the
  * function at values outside of this range generate IllegalArgumentExceptions.
  * <p>
  * The value of the polynomial spline function for an argument <code>x</code>
@@ -44,7 +44,7 @@ import org.apache.commons.math.FunctionEvaluationException;
  * <ol>
  * <li>The knot array is searched to find the segment to which <code>x</code>
  * belongs.  If <code>x</code> is less than the smallest knot point or greater
- * than or equal to the largest one, an <code>IllegalArgumentException</code>
+ * than the largest one, an <code>IllegalArgumentException</code>
  * is thrown.</li>
  * <li> Let <code>j</code> be the index of the largest knot point that is less
  * than or equal to <code>x</code>.  The value returned is <br>
@@ -116,7 +116,7 @@ public class PolynomialSplineFunction implements UnivariateRealFunction, Seriali
      * Compute the value for the function.
      * <p>
      * Throws FunctionEvaluationException if v is outside of the domain of the
-     * function.  The domain is [smallest knot, largest knot).
+     * function.  The domain is [smallest knot, largest knot].
      * <p>
      * See {@link PolynomialSplineFunction} for details on the algorithm for
      * computing the value of the function.
@@ -125,16 +125,22 @@ public class PolynomialSplineFunction implements UnivariateRealFunction, Seriali
      * @return the value
      * @throws FunctionEvaluationException if v is outside of the domain of
      * of the spline function (less than the smallest knot point or greater
-     * than or equal to the largest knot point)
+     * than the largest knot point)
      */
     public double value(double v) throws FunctionEvaluationException {
-        if (v < knots[0] || v >= knots[n]) {
+        if (v < knots[0] || v > knots[n]) {
             throw new FunctionEvaluationException(v,"Argument outside domain");
         }
         int i = Arrays.binarySearch(knots, v);
         if (i < 0) {
             i = -i - 2;
         }
+        //This will handle the case where v is the last knot value
+        //There are only n-1 polynomials, so if v is the last knot
+        //then we will use the last polynomial to calculate the value.
+        if ( i >= polynomials.length ) {
+            i--;
+        }
         return polynomials[i].value(v - knots[i]);
     }
     

src/test/org/apache/commons/math/analysis/SplineInterpolatorTest.java

@@ -67,7 +67,9 @@ public class SplineInterpolatorTest extends TestCase {
         TestUtils.assertEquals(polynomials[1].getCoefficients(), target, coefficientTolerance);
         
         // Check interpolation
+        assertEquals(0.0,f.value(0.0), interpolationTolerance);
         assertEquals(0.4,f.value(0.4), interpolationTolerance);
+        assertEquals(1.0,f.value(1.0), interpolationTolerance);
     }
 
     public void testInterpolateLinearDegenerateThreeSegment()
@@ -88,7 +90,9 @@ public class SplineInterpolatorTest extends TestCase {
         TestUtils.assertEquals(polynomials[2].getCoefficients(), target, coefficientTolerance);
         
         // Check interpolation
+        assertEquals(0,f.value(0), interpolationTolerance);
         assertEquals(1.4,f.value(1.4), interpolationTolerance);
+        assertEquals(1.5,f.value(1.5), interpolationTolerance);
     }
 
     public void testInterpolateLinear() throws Exception {
@@ -179,11 +183,11 @@ public class SplineInterpolatorTest extends TestCase {
     }
     
     /**
-     * verifies that f(x[i]) = y[i] for i = 0..n -1 where n is common length -- skips last point.
+     * verifies that f(x[i]) = y[i] for i = 0..n-1 where n is common length.
      */
     protected void verifyInterpolation(UnivariateRealFunction f, double x[], double y[])  
     	throws Exception{
-        for (int i = 0; i < x.length - 1; i++) {
+        for (int i = 0; i < x.length; i++) {
             assertEquals(f.value(x[i]), y[i], knotTolerance);
         }     
     }

xdocs/changes.xml

@@ -39,6 +39,10 @@ The <action> type attribute can be add,update,fix,remove.
   <body>
     <release version="1.1" date="In Development"  
        description="Jakarta Commons Math 1.1 - Development">
+      <action dev="brentworden" type="fix" due-to="Ben Litchfield">
+        Fixed bug in PolynomialSplineFunction to allow evaluation of the
+		function at the last knot point.
+      </action>
       <action dev="brentworden" type="add">
         Added Weibull distribution implementation.
       </action>