NUMBER-46: Meaning of "maxIterations" argument.
Project: http://git-wip-us.apache.org/repos/asf/commons-numbers/repo Commit: http://git-wip-us.apache.org/repos/asf/commons-numbers/commit/bc83d14f Tree: http://git-wip-us.apache.org/repos/asf/commons-numbers/tree/bc83d14f Diff: http://git-wip-us.apache.org/repos/asf/commons-numbers/diff/bc83d14f Branch: refs/heads/master Commit: bc83d14fe2b7b4e86f6b01d37ce6b92bbf468916 Parents: 47e19ab Author: Gilles Sadowski <[email protected]> Authored: Mon Jul 3 16:08:19 2017 +0200 Committer: Gilles Sadowski <[email protected]> Committed: Mon Jul 3 16:08:19 2017 +0200 ---------------------------------------------------------------------- .../numbers/fraction/ContinuedFraction.java | 28 ++++++------- .../numbers/fraction/ContinuedFractionTest.java | 44 +++++++++++++++++++- 2 files changed, 54 insertions(+), 18 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/commons-numbers/blob/bc83d14f/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/ContinuedFraction.java ---------------------------------------------------------------------- diff --git a/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/ContinuedFraction.java b/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/ContinuedFraction.java index 47bd9b9..5c5648d 100644 --- a/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/ContinuedFraction.java +++ b/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/ContinuedFraction.java @@ -80,7 +80,7 @@ public abstract class ContinuedFraction { } /** - * Evaluates the continued fraction at the value x. + * Evaluates the continued fraction. * <p> * The implementation of this method is based on the modified Lentz algorithm as described * on page 18 ff. in: @@ -99,12 +99,13 @@ public abstract class ContinuedFraction { * <a href="http://mathworld.wolfram.com/ContinuedFraction.html";>Continued Fraction @ MathWorld</a>. * </p> * - * @param x the evaluation point. - * @param epsilon maximum error allowed. - * @param maxIterations maximum number of convergents - * @return the value of the continued fraction evaluated at x. + * @param x Point at which to evaluate the continued fraction. + * @param epsilon Maximum error allowed. + * @param maxIterations Maximum number of iterations. + * @return the value of the continued fraction evaluated at {@code x}. * @throws ArithmeticException if the algorithm fails to converge. - * @throws ArithmeticException if maximal number of iterations is reached + * @throws ArithmeticException if the maximal number of iterations is reached + * before the expected convergence is achieved. */ public double evaluate(double x, double epsilon, int maxIterations) { final double small = 1e-50; @@ -120,7 +121,7 @@ public abstract class ContinuedFraction { double cPrev = hPrev; double hN = hPrev; - while (n < maxIterations) { + while (n <= maxIterations) { final double a = getA(n, x); final double b = getB(n, x); @@ -146,21 +147,16 @@ public abstract class ContinuedFraction { x); } - if (Math.abs(deltaN - 1.0) < epsilon) { - break; + if (Math.abs(deltaN - 1) < epsilon) { + return hN; } dPrev = dN; cPrev = cN; hPrev = hN; - n++; - } - - if (n >= maxIterations) { - throw new FractionException("maximal count ({0}) exceeded", maxIterations); + ++n; } - return hN; + throw new FractionException("maximal count ({0}) exceeded", maxIterations); } - } http://git-wip-us.apache.org/repos/asf/commons-numbers/blob/bc83d14f/commons-numbers-fraction/src/test/java/org/apache/commons/numbers/fraction/ContinuedFractionTest.java ---------------------------------------------------------------------- diff --git a/commons-numbers-fraction/src/test/java/org/apache/commons/numbers/fraction/ContinuedFractionTest.java b/commons-numbers-fraction/src/test/java/org/apache/commons/numbers/fraction/ContinuedFractionTest.java index 8f450aa..8543f0a 100644 --- a/commons-numbers-fraction/src/test/java/org/apache/commons/numbers/fraction/ContinuedFractionTest.java +++ b/commons-numbers-fraction/src/test/java/org/apache/commons/numbers/fraction/ContinuedFractionTest.java @@ -28,8 +28,47 @@ public class ContinuedFractionTest { @Test public void testGoldenRatio() throws Exception { ContinuedFraction cf = new ContinuedFraction() { + @Override + public double getA(int n, double x) { + return 1; + } @Override + public double getB(int n, double x) { + return 1; + } + }; + + final double eps = 1e-8; + double gr = cf.evaluate(0, eps); + Assert.assertEquals(1.61803399, gr, eps); + } + + // NUMBERS-46 + @Test + public void testOneIteration() { + ContinuedFraction cf = new ContinuedFraction() { + @Override + public double getA(int n, double x) { + return 1; + } + + @Override + public double getB(int n, double x) { + return 1; + } + }; + + final double eps = 10; + double gr = cf.evaluate(0, eps, 1); + Assert.assertEquals(1.61, gr, eps); + } + + // NUMBERS-46 + @Test + public void testTwoIterations() { + ContinuedFraction cf = new ContinuedFraction() { + @Override public double getA(int n, double x) { return 1; } @@ -40,7 +79,8 @@ public class ContinuedFractionTest { } }; - double gr = cf.evaluate(0.0, 1e-8); - Assert.assertEquals(1.61803399, gr, 1e-8); + final double eps = 0.5; + double gr = cf.evaluate(0, eps, 2); + Assert.assertEquals(1.5, gr, 0d); } }
