cauchy_kernel.hpp

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/*
 * PoPS model - cauchy dispersal kernel
 *
 * Copyright (C) 2015-2020 by the authors.
 *
 * Authors: Margaret Lawrimore malawrim ncsu edu
 *
 * The code contained herein is licensed under the GNU General Public
 * License. You may obtain a copy of the GNU General Public License
 * Version 2 or later at the following locations:
 *
 * http://www.opensource.org/licenses/gpl-license.html
 * http://www.gnu.org/copyleft/gpl.html
 */
 
#ifndef POPS_CAUCHY_KERNEL_HPP
#define POPS_CAUCHY_KERNEL_HPP
 
#include "utils.hpp"
#include "kernel_types.hpp"
#include "raster.hpp"
 
#include <random>
 
namespace pops {
 
using std::pow;
using std::tan;
 
class CauchyKernel
{
protected:
    double s;
    std::cauchy_distribution<double> cauchy_distribution;
 
public:
    CauchyKernel(double scale) : s(scale), cauchy_distribution(0, s)
    {
        if (scale <= 0) {
            throw std::invalid_argument(
                "CauchyKernel: scale (s) must be greater than 0.0");
        }
    }
 
    template<class Generator>
    double random(Generator& generator)
    {
        return std::abs(cauchy_distribution(generator));
    }
 
    double pdf(double x)
    {
        return 1 / ((s * M_PI) * (1 + (pow(x / s, 2))));
    }
 
    double icdf(double x)
    {
        if (x <= 0 || x >= 1) {
            throw std::invalid_argument("icdf: x must be between 0.0 and 1.0");
        }
        return s * tan(M_PI * (x - 0.5));
    }
};
 
}  // namespace pops
 
#endif  // POPS_CAUCHY_KERNEL_HPP