text: // Arguments: Doubles, Doubles, Doubles
  #include <stan/math/prim.hpp>
  
  using stan::math::var;
  using std::numeric_limits;
  using std::vector;
  
  class AgradCcdfLogFrechet : public AgradCcdfLogTest {
   public:
    void valid_values(vector<vector<double> >& parameters,
                      vector<double>& ccdf_log) {
      vector<double> param(3);
  
      param[0] = 2.0;  // y
      param[1] = 1.0;  // alpha
      param[2] = 1.0;  // sigma
      parameters.push_back(param);
      ccdf_log.push_back(
          std::log(0.3934693402873665757369));  // expected ccdf_log
  
      param[0] = 3.9;   // y
      param[1] = 1.7;   // alpha
      param[2] = 0.25;  // sigma
      parameters.push_back(param);
      ccdf_log.push_back(-4.675041342361127);  // expected ccdf_log
    }
  
    void invalid_values(vector<size_t>& index, vector<double>& value) {
      // y
      index.push_back(0U);
      value.push_back(-1.0);
  
      index.push_back(0U);
      value.push_back(-numeric_limits<double>::infinity());
  
      // alpha
      index.push_back(1U);
      value.push_back(numeric_limits<double>::infinity());
  
      index.push_back(1U);
      value.push_back(-numeric_limits<double>::infinity());
  
      // sigma
      index.push_back(2U);
      value.push_back(0.0);
  
      index.push_back(2U);
      value.push_back(-1.0);
    }
  
    bool has_lower_bound() { return true; }
  
    double lower_bound() { return 1e-322; }
  
    bool has_upper_bound() { return false; }
  
    template <typename T_y, typename T_shape, typename T_scale, typename T3,
              typename T4, typename T5>
    stan::return_type_t<T_y, T_shape, T_scale> ccdf_log(const T_y& y,
                                                        const T_shape& alpha,
                                                        const T_scale& sigma,
                                                        const T3&, const T4&,
                                                        const T5&) {
      return stan::math::frechet_ccdf_log(y, alpha, sigma);
    }
  
    template <typename T_y, typename T_shape, typename T_scale, typename T3,
              typename T4, typename T5>
    stan::return_type_t<T_y, T_shape, T_scale> ccdf_log_function(
        const T_y& y, const T_shape& alpha, const T_scale& sigma, const T3&,
        const T4&, const T5&) {
      using std::exp;
      using std::log;
      using std::pow;
      return log(1.0 - exp(-pow(sigma / y, alpha)));
    }
  };
  