bounds_on_ratios_in_sampled_sets.hpp

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
 
#ifndef BOUNDS_ON_RATIOS_IN_SAMPLED_SETS_HPP_
#define BOUNDS_ON_RATIOS_IN_SAMPLED_SETS_HPP_
 
#include <cstdint>
#include <string>
#include <stdexcept>
 
#include "bounds_binomial_proportions.hpp"
 
namespace datasketches {
 
class bounds_on_ratios_in_sampled_sets {
public:
  static constexpr double NUM_STD_DEVS = 2.0;
 
  static double lower_bound_for_b_over_a(uint64_t a, uint64_t b, double f) {
    check_inputs(a, b, f);
    if (a == 0) return 0.0;
    if (f == 1.0) return static_cast<double>(b) / static_cast<double>(a);
    return bounds_binomial_proportions::approximate_lower_bound_on_p(a, b, NUM_STD_DEVS * hacky_adjuster(f));
  }
 
  static double upper_bound_for_b_over_a(uint64_t a, uint64_t b, double f) {
    check_inputs(a, b, f);
    if (a == 0) return 1.0;
    if (f == 1.0) return static_cast<double>(b) / static_cast<double>(a);
    return bounds_binomial_proportions::approximate_upper_bound_on_p(a, b, NUM_STD_DEVS * hacky_adjuster(f));
  }
 
  static double get_estimate_of_b_over_a(uint64_t a, uint64_t b) {
    check_inputs(a, b, 0.3);
    if (a == 0) return 0.5;
    return static_cast<double>(b) / static_cast<double>(a);
  }
 
  static double estimate_of_a(uint64_t a, double f) {
    check_inputs(a, 1, f);
    return a / f;
  }
 
  static double estimate_of_b(uint64_t b, double f) {
    check_inputs(b + 1, b, f);
    return b / f;
  }
 
private:
  static double hacky_adjuster(double f) {
    const double tmp = sqrt(1.0 - f);
    return (f <= 0.5) ? tmp : tmp + (0.01 * (f - 0.5));
  }
 
  static void check_inputs(uint64_t a, uint64_t b, double f) {
    if (a < b) {
      throw std::invalid_argument("a must be >= b: a = " + std::to_string(a) + ", b = " + std::to_string(b));
    }
    if ((f > 1.0) || (f <= 0.0)) {
      throw std::invalid_argument("Required: ((f <= 1.0) && (f > 0.0)): " + std::to_string(f));
    }
  }
 
};
 
} /* namespace datasketches */
 
# endif