public int inverseCumulativeProbability()

in commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/GeometricDistribution.java [147:174]

• 16 lines of code
• 6 McCabe index (conditional complexity)

    public int inverseCumulativeProbability(double p) {
        ArgumentUtils.checkProbability(p);
        if (p == 1) {
            return getSupportUpperBound();
        }
        if (p <= probabilityOfSuccess) {
            return 0;
        }
        // p > probabilityOfSuccess
        // => log(1-p) < log(1-probabilityOfSuccess);
        // Both terms are negative as probabilityOfSuccess > 0.
        // This should be lower bounded to (2 - 1) = 1
        int x = (int) (Math.ceil(Math.log1p(-p) / log1mProbabilityOfSuccess) - 1);

        // Correct rounding errors.
        // This ensures x == icdf(cdf(x))

        if (cumulativeProbability(x - 1) >= p) {
            // No checks for x=0.
            // If x=0; cdf(-1) = 0 and the condition is false as p>0 at this point.
            x--;
        } else if (cumulativeProbability(x) < p && x < Integer.MAX_VALUE) {
            // The supported upper bound is max_value here as probabilityOfSuccess != 1
            x++;
        }

        return x;
    }