private double searchPlateau()

in commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/AbstractContinuousDistribution.java [376:407]

• 26 lines of code
• 9 McCabe index (conditional complexity)

    private double searchPlateau(boolean complement, double lower, final double x) {
        // Test for plateau. Lower the value x if the probability is the same.
        // Ensure the step is robust to the solver accuracy being less
        // than 1 ulp of x (e.g. dx=0 will infinite loop)
        final double dx = Math.max(SOLVER_ABSOLUTE_ACCURACY, Math.ulp(x));
        if (x - dx >= lower) {
            final DoubleUnaryOperator fun = complement ?
                this::survivalProbability :
                this::cumulativeProbability;
            final double px = fun.applyAsDouble(x);
            if (fun.applyAsDouble(x - dx) == px) {
                double upperBound = x;
                double lowerBound = lower;
                // Bisection search
                // Require cdf(x) < px and sf(x) > px to move the lower bound
                // to the midpoint.
                final DoubleBinaryOperator cmp = complement ?
                    (a, b) -> a > b ? -1 : 1 :
                    (a, b) -> a < b ? -1 : 1;
                while (upperBound - lowerBound > dx) {
                    final double midPoint = 0.5 * (lowerBound + upperBound);
                    if (cmp.applyAsDouble(fun.applyAsDouble(midPoint), px) < 0) {
                        lowerBound = midPoint;
                    } else {
                        upperBound = midPoint;
                    }
                }
                return upperBound;
            }
        }
        return x;
    }