UtilFunctions.h

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#include <iostream>
#include <map>
#include "backends/interfaces/IRandomNumberGenerator.h"
 
namespace quisp::util_functions {
using quisp::backends::abstract::IRandomNumberGenerator;
 
/*
  Description:
    This is a function that, given a set of labels and weights and a random number, returns a label according to the random number
  Args:
    std::map<Label, double> weights: weight(double) and label are a pair of values and it is a elements of std:map.
    rand: random number(double)
  Return:
    It returns label probabilistically according to the weights.
  Example:
    weight = {{ErrorLabel::X, 0.3}, {ErrorLabel::Z, 0.4}, {ErrorLabel::Y, 0.3}}}
    rand = 0.4
 
    returns ErrorLabel::Z
 */
template <typename Label>
Label samplingWithWeights(std::map<Label, double> weights, double rand) {
  double sum = 0;
  for (auto &[l, w] : weights) {
    sum += w;
  }
  double ceil = 0;
  for (auto &[l, w] : weights) {
    ceil += w / sum;
 
    if (rand <= ceil) {
      return l;
    }
  }
  return (--weights.end())->first;
}
}  // namespace quisp::util_functions