screening_kernels.h

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/*
 *            Copyright 2009-2026 The VOTCA Development Team
 *                       (http://www.votca.org)
 *
 *      Licensed under the Apache License, Version 2.0 (the "License")
 *
 * You may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *              http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */
 
#pragma once
#ifndef VOTCA_XTP_SCREENING_KERNELS_H
#define VOTCA_XTP_SCREENING_KERNELS_H
 
// Standard includes
#include <functional>
#include <optional>
#include <string>
 
// Local VOTCA includes
#include "dfttimings.h"
#include "eigen.h"
 
namespace votca {
namespace xtp {

class WeightedGram {
 public:
  using RowsVisitor =
      std::function<void(const Eigen::Ref<const Eigen::MatrixXd>&)>;
  using RowsFn = std::function<void(Index m, const RowsVisitor& use)>;
  using WeightsFn = std::function<void(Index m, Eigen::VectorXd& w)>;

  static void setBatchMemory(double bytes) { batch_bytes_ = bytes; }
 
  static Eigen::MatrixXd Compute(Index nblocks, Index ncols,
                                 const WeightsFn& weights, const RowsFn& rows);
 
 private:
  static double batch_bytes_;
};

struct SymmetricEigenSystem {
  Eigen::VectorXd values;
  Eigen::MatrixXd vectors;
};

SymmetricEigenSystem SymmetricEigen(const Eigen::MatrixXd& A,
                                    bool vectors = true);

class CholeskyFactor {
 public:
  CholeskyFactor() = default;
  explicit CholeskyFactor(const Eigen::MatrixXd& A);
  void compute(const Eigen::MatrixXd& A);
  bool ok() const { return ok_; }
  const Eigen::MatrixXd& matrixL() const { return L_; }
  Eigen::MatrixXd SolveL(const Eigen::MatrixXd& B) const;
  Eigen::MatrixXd Solve(const Eigen::MatrixXd& B) const;
 
 private:
  Eigen::MatrixXd L_;
  bool ok_ = false;
};

Eigen::MatrixXd InverseSPD(const Eigen::MatrixXd& A);

class OptionalTiming {
 public:
  OptionalTiming(DFTTimings* timings, const std::string& name) {
    if (timings != nullptr && !OPENMP::InsideActiveParallelRegion()) {
      scope_.emplace(*timings, name);
    }
  }
 
 private:
  std::optional<DFTTimings::Scope> scope_;
};
 
}  // namespace xtp
}  // namespace votca
 
#endif  // VOTCA_XTP_SCREENING_KERNELS_H