Alex Herbert created NUMBERS-176:
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Summary: ContinuedFraction to delegate to
GeneralizedContinuedFraction
Key: NUMBERS-176
URL: https://issues.apache.org/jira/browse/NUMBERS-176
Project: Commons Numbers
Issue Type: Improvement
Components: fraction
Affects Versions: 1.1
Reporter: Alex Herbert
The ContinuedFraction class evaluates using the same algorithm as the
GeneralizedContinuedFraction. These should use the same code to eliminate
duplication.
The GeneralizedContinuedFraction has the latest version of the algorithm with a
bug fix for detecting invalid update steps and increased support for very small
convergence epsilon (see NUMBERS-175).
The simple approach is to call the GeneralizedContinuedFraction by creating a
generator from the ContinuedFraction and the argument x:
{code:java}
public double evaluate(double x, double epsilon, int maxIterations) {
// Delegate to GeneralizedContinuedFraction
// Get the first coefficient
final double b0 = getB(0, x);
// Generate coefficients from (a1,b1)
final Supplier<Coefficient> gen = new Supplier<Coefficient>() {
private int n;
@Override
public Coefficient get() {
n++;
final double a = getA(n, x);
final double b = getB(n, x);
return Coefficient.of(a, b);
}
};
// Invoke appropriate method based on magnitude of first term
if (Math.abs(b0) < SMALL) {
return GeneralizedContinuedFraction.value(b0, gen, epsilon,
maxIterations);
}
return GeneralizedContinuedFraction.evaluate(b0, gen, epsilon,
maxIterations);
}
{code}
This will only evaluate each used coefficient once. It requires exposure of the
GeneralizedContinuedFraction.evaluate method at the package level.
The threshold for small values and default for iterations can be exposed as
package private from GeneralizedContinuedFraction. This ensures the method
calls the appropriate evaluation method based on the magnitude of the first
term b0 with the same defaults.
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