VariableTransformation.h

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#pragma once
 
#include <cmath>
 
namespace ProcessLib
{
 
struct TrafoLog
{
    static const bool constrained = true;
 
    static double x(const double y) { return std::exp(y); }
 
    static double dxdy(const double x) { return x; }
};
 
struct TrafoIdentity
{
    static const bool constrained = false;
 
    static double x(const double y) { return y; }
 
    static double dxdy(const double /*x*/) { return 1.0; }
};
 
struct TrafoTanh
{
    static const bool constrained = true;
 
    static double x(const double y) { return 0.5 * std::tanh(y) + 0.5; }
 
    static double dxdy(const double x) { return 2.0 * x * (1.0 - x); }
};
 
struct TrafoScale
{
    explicit TrafoScale(const double factor) : _factor{factor} {}
 
    static const bool constrained = false;
 
    double x(const double y) const { return y * _factor; }
 
    double y(const double x) const { return x / _factor; }
 
    double dxdy(const double /*x*/) const { return _factor; }
 
private:
    double _factor;
};
 
using Trafo = ProcessLib::TrafoScale;
}  // namespace ProcessLib