ROL_LogExponentialQuadrangle.hpp

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#ifndef ROL_LOGEXPONENTIALQUAD_HPP
#define ROL_LOGEXPONENTIALQUAD_HPP

#include "ROL_ExpectationQuad.hpp"

namespace ROL {

template<class Real>
class LogExponentialQuadrangle : public ExpectationQuad<Real> {
private:
  Real coeff_;

  void parseParameterList(ROL::ParameterList &parlist) {
    std::string type = parlist.sublist("SOL").get("Stochastic Component Type","Risk Averse");
    ROL::ParameterList list;
    if (type == "Risk Averse") {
      list = parlist.sublist("SOL").sublist("Risk Measure").sublist("Entropic Risk");
    }
    else if (type == "Error") {
      list = parlist.sublist("SOL").sublist("Error Measure").sublist("Exponential");
    }
    else if (type == "Deviation") {
      list = parlist.sublist("SOL").sublist("Deviation Measure").sublist("Entropic");
    }
    else if (type == "Regret") {
      list = parlist.sublist("SOL").sublist("Regret Measure").sublist("Exponential");
    }
    coeff_ = list.get<Real>("Rate");
  }

  void checkInputs(void) const {
    Real zero(0);
    ROL_TEST_FOR_EXCEPTION((coeff_ <= zero), std::invalid_argument,
      ">>> ERROR (ROL::LogExponentialQuadrangle): Rate must be positive!");
  }

public:
  LogExponentialQuadrangle(const Real coeff = 1)
    : ExpectationQuad<Real>(), coeff_(coeff) {
    checkInputs();
  }

  LogExponentialQuadrangle(ROL::ParameterList &parlist)
    : ExpectationQuad<Real>() {
    parseParameterList(parlist);
    checkInputs();
  }

  Real error(Real x, int deriv = 0) {
    Real err(0), one(1), cx = coeff_*x;
    if (deriv==0) {
      err = (std::exp(cx) - cx - one)/coeff_;
    }
    else if (deriv==1) {
      err = std::exp(cx) - one;
    }
    else {
      err = coeff_*std::exp(cx);
    }
    return err;
  }

  Real regret(Real x, int deriv = 0) {
    Real zero(0), one(1);
    Real X = ((deriv==0) ? x : ((deriv==1) ? one : zero));
    Real reg = error(x,deriv) + X;
    return reg;
  }

};

}
#endif