Add Spectra.

thirdparty/include/Spectra/LinAlg/SearchSpace.h

@@ -0,0 +1,96 @@
+// Copyright (C) 2020 Netherlands eScience Center <n.renauld@esciencecenter.nl>
+//
+// This Source Code Form is subject to the terms of the Mozilla
+// Public License v. 2.0. If a copy of the MPL was not distributed
+// with this file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+#ifndef SPECTRA_SEARCH_SPACE_H
+#define SPECTRA_SEARCH_SPACE_H
+
+#include <Eigen/Core>
+
+#include "RitzPairs.h"
+#include "Orthogonalization.h"
+
+namespace Spectra {
+
+/// This class handles the creation and manipulation of the search space
+/// for iterative eigensolvers such as Davidson, Jacobi-Davidson, etc.
+template <typename Scalar>
+class SearchSpace
+{
+private:
+    using Index = Eigen::Index;
+    using Matrix = Eigen::Matrix<Scalar, Eigen::Dynamic, Eigen::Dynamic>;
+
+    Matrix m_basis_vectors;
+    Matrix m_op_basis_product;
+
+    /// Append new vector to the basis
+    ///
+    /// \param new_vect Matrix of new correction vectors
+    void append_new_vectors_to_basis(const Matrix& new_vect)
+    {
+        Index num_update = new_vect.cols();
+        m_basis_vectors.conservativeResize(Eigen::NoChange, m_basis_vectors.cols() + num_update);
+        m_basis_vectors.rightCols(num_update).noalias() = new_vect;
+    }
+
+public:
+    SearchSpace() = default;
+
+    /// Returns the current size of the search space
+    Index size() const { return m_basis_vectors.cols(); }
+
+    void initialize_search_space(const Eigen::Ref<const Matrix>& initial_vectors)
+    {
+        m_basis_vectors = initial_vectors;
+        m_op_basis_product = Matrix(initial_vectors.rows(), 0);
+    }
+
+    /// Updates the matrix formed by the operator applied to the search space
+    /// after the addition of new vectors in the search space. Only the product
+    /// of the operator with the new vectors is computed and the result is appended
+    /// to the op_basis_product member variable
+    ///
+    /// \param OpType Operator representing the matrix
+    template <typename OpType>
+    void update_operator_basis_product(OpType& op)
+    {
+        Index nvec = m_basis_vectors.cols() - m_op_basis_product.cols();
+        m_op_basis_product.conservativeResize(Eigen::NoChange, m_basis_vectors.cols());
+        m_op_basis_product.rightCols(nvec).noalias() = op * m_basis_vectors.rightCols(nvec);
+    }
+
+    /// Restart the search space by reducing the basis vector to the last
+    /// Ritz eigenvector
+    ///
+    /// \param ritz_pair Instance of a RitzPair class
+    /// \param size Size of the restart
+    void restart(const RitzPairs<Scalar>& ritz_pairs, Index size)
+    {
+        m_basis_vectors = ritz_pairs.ritz_vectors().leftCols(size);
+        m_op_basis_product = m_op_basis_product * ritz_pairs.small_ritz_vectors().leftCols(size);
+    }
+
+    /// Append new vectors to the search space and
+    /// orthogonalize the resulting matrix
+    ///
+    /// \param new_vect Matrix of new correction vectors
+    void extend_basis(const Matrix& new_vect)
+    {
+        Index left_cols_to_skip = size();
+        append_new_vectors_to_basis(new_vect);
+        twice_is_enough_orthogonalisation(m_basis_vectors, left_cols_to_skip);
+    }
+
+    /// Returns the basis vectors
+    const Matrix& basis_vectors() const { return m_basis_vectors; }
+
+    /// Returns the operator applied to basis vector
+    const Matrix& operator_basis_product() const { return m_op_basis_product; }
+};
+
+}  // namespace Spectra
+
+#endif  // SPECTRA_SEARCH_SPACE_H