- * @brief Select a branch from the given predicate branches based
- * on their exploration counts.
- *
- * Let b_1, ..., b_n be branches with exploration counts c_1, ..., c_n
- * M := max(c_1, ..., c_n) + 1
- * Factor f_i := M / (c_i + 1)
- * The probability p_i that branch b_i is selected:
- * p_i := f_i / (f_1 + ... + f_n)
- * = \fraction{ 1/(c_i + 1) }{ 1/(c_1 + 1) + ... + 1/(c_n + 1) }
- *
- * Note: (1) c_i + 1 is used because counts may be 0.
- * (2) The numerator of f_i is chosen to reduce the effect of underflow
- *
- * @param numerator is M defined above