CIEnvironment.hpp

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// This file is part of GQCG-GQCP.
//
// Copyright (C) 2017-2020  the GQCG developers
//
// GQCG-GQCP is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// GQCG-GQCP is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with GQCG-GQCP.  If not, see <http://www.gnu.org/licenses/>.
 
#pragma once
 
 
#include "Mathematical/Optimization/Eigenproblem/EigenproblemEnvironment.hpp"
 
 
namespace GQCP {
namespace CIEnvironment {
 
 
template <typename Hamiltonian, typename ONVBasis>
auto Dense(const Hamiltonian& hamiltonian, const ONVBasis& onv_basis) -> EigenproblemEnvironment<typename Hamiltonian::Scalar> {
 
    using Scalar = typename Hamiltonian::Scalar;  // The scalar type of a Hamiltonian element.
 
    // Determine the dense matrix representation of the Hamiltonian in the given ONV basis, and supply it to an `EigenproblemEnvironment`.
    const auto H = onv_basis.evaluateOperatorDense(hamiltonian);
    return EigenproblemEnvironment<Scalar>::Dense(H);
}
 
 
template <typename Hamiltonian, typename ONVBasis>
EigenproblemEnvironment<double> Iterative(const Hamiltonian& hamiltonian, const ONVBasis& onv_basis, const MatrixX<double>& V) {
 
    // Determine the diagonal of the Hamiltonian matrix representation, and supply a matrix-vector product function to the `EigenproblemEnvironment`.
    const auto diagonal = onv_basis.evaluateOperatorDiagonal(hamiltonian);
    const auto matvec_function = [&hamiltonian, &onv_basis](const VectorX<double>& x) { return onv_basis.evaluateOperatorMatrixVectorProduct(hamiltonian, x); };
 
    return EigenproblemEnvironment<double>::Iterative(matvec_function, diagonal, V);
}
 
 
}  // namespace CIEnvironment
}  // namespace GQCP