absorbing_ends.h

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#ifndef ABSORBING_ENDS_H
#define ABSORBING_ENDS_H
 
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
 
#include "node.h"
 
struct AbsorbingEnds
    {
    bool enable = false;
 
    Nodes::index axis = Nodes::IDX_Z;
 
    double length = 0;
 
    double alpha_max = 1;
 
    std::vector<std::string> regions;
 
    double lo = 0;
 
    double hi = 0;
 
    double alpha(const double alpha0, const double x) const
        {
        if (!enable)
            { return alpha0; }
        const double s = std::max(x - (hi - length), (lo + length) - x);  // depth in the nearest zone
        if (s <= 0)
            { return alpha0; }
        const double sn = std::sin(M_PI_2 * std::min(s / length, 1.0));
        return alpha0 + (alpha_max - alpha0) * sn * sn;
        }
    };
 
#endif