/usr/include/chemps2/ConjugateGradient.h is in libchemps2-dev 1.8.3-2.
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CheMPS2: a spin-adapted implementation of DMRG for ab initio quantum chemistry
Copyright (C) 2013-2016 Sebastian Wouters
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#ifndef CONJUGATEGRADIENT_CHEMPS2_H
#define CONJUGATEGRADIENT_CHEMPS2_H
namespace CheMPS2{
/** Conjugate gradient class.
\author Sebastian Wouters <sebastianwouters@gmail.com>
\date January 27, 2016
The ConjugateGradient class implements the conjugate gradient algorithm to solve the symmetric linear problem \n
\f$ operator * x = b \f$. \n
With precon = 1 / sqrt( diag( operator ) ), the problem is turned into \n
\f$ precon * operator * precon * xtilde = precon * b \f$ \n
\f$ x = precon * xtilde \f$.
*/
class ConjugateGradient{
public:
//! Constructor
/** \param veclength_in Linear dimension of the symmetric matrix
\param RTOL_in The tolerance for the two-norm of the residual
\param DIAG_CUTOFF_in The cutoff to truncate the diagonal elements of operator
\param print_in Whether or not to print */
ConjugateGradient(const int veclength_in, const double RTOL_in, const double DIAG_CUTOFF_in, const bool print_in);
//! Destructor
virtual ~ConjugateGradient();
//! The iterator to converge the ground state vector
/** \param pointers Array of double* of length 3 to return pointers to vectors to the caller
\return Instruction character. 'A' means copy the initial guess to pointers[0], the diagonal of the symmetric matrix to pointers[1], and the right-hand side of the problem to pointers[2]. 'B' means calculate pointers[1] = symmetric matrix times pointers[0]. 'C' means that the converged solution can be copied back from pointers[0], and the residual norm from pointers[1][0]. 'D' means that an error has occurred. */
char step( double ** pointers );
//! Get the number of matrix vector multiplications which have been performed
/** \return The number of matrix vector multiplications which have been performed */
int get_num_matvec() const;
private:
int veclength;
double RTOL;
double DIAG_CUTOFF;
bool print;
char state; // Current state of the algorithm
int num_matvec; // Current number of matvec multiplications
// Helper arrays
double * XVEC;
double * PRECON;
double * RHS;
double * WORK;
double * RESID;
double * PVEC;
double * OPVEC;
// Helper variables
double rnorm;
double rdotr;
// Internal functions to hop between states
void stepL2K();
void stepY2Z();
void stepJ2K();
void stepG2H();
double inprod( double * vector );
double inprod( double * vector, double * othervector );
void apply_precon( double * vector );
void apply_precon( double * vector, double * result );
};
}
#endif
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