SigmoidFunction.cpp

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#include "SigmoidFunction.h"
 
namespace MaterialPropertyLib
{
SigmoidFunction::SigmoidFunction(double const k, double const T_c,
                                 double const S_r)
    : k_(k), T_c_(T_c), S_r(S_r)
{
}
 
double SigmoidFunction::value(double const& T) const
{
    double const x = k_ * (T - T_c_);
 
    // Cutting off at the last x producing a (non-normal) return value because
    // std::exp(x) produces +infinity beyond this point, approximately 709.78.
    // The reason for using hex representation is that the value is unambiguous.
    if (x > 0x1.62e42fefa39efp+9)
    {
        return 0.;
    }
 
    return (1. - S_r) / (1. + std::exp(x));
}
 
double SigmoidFunction::dValue(double const& T) const
{
    double const f = value(T);
    if (f * f == 0)
    {
        return 0;
    }
    double const x = k_ * (T - T_c_);
    return -k_ * std::exp(x) * (f * f) / (1. - S_r);
}
 
double SigmoidFunction::d2Value(double const& T) const
{
    double const fT = dValue(T);
    if (fT == 0)
    {
        return 0;
    }
 
    double const f = value(T);
    return fT * (k_ + 2 * fT / f);
}
 
}  // namespace MaterialPropertyLib