DMRG::BROOM Struct Reference

Detailed Description

Choice of tool to perfom the sweeping.

Definition at line 259 of file DmrgTypedefs.h.

#include <DmrgTypedefs.h>

Public Types
enum	OPTION {   QR , SVD , BRUTAL_SVD , RDM ,   RICH_SVD , QR_NULL }

Member Enumeration Documentation

OPTION

enum DMRG::BROOM::OPTION

Enumerator
QR	Uses the QR decomposition. It is the fastest of all options, but preserves the matrix sizes, so that neither truncation nor growth can occur. Since the singular values are not computed, no entropy can be calculated and is therefore set to nan.
SVD	Uses the singular value decomposition. All singular values below eps_truncWeight are cut off. Warning Needs Lapack. Define DONT_USE_LAPACK_SVD to use Eigen's SVD routine. It is 3-90 times slower, but probably accurate and stable as hell.
BRUTAL_SVD	Uses the singular value decomposition, but imposes a limit on the matrix sizes. Only the first DmrgJanitor::N_sv singular values per symmetry block are kept. This option can be useful to generate starting points for variational procedures. Warning Needs Lapack (see above).
RDM	Uses diagonalization of the reduced density matrix. Adds a noise term multiplied by DmrgJanitor::eps_noise. All eigenvalues smaller than DmrgJanitor::eps_rdm are cut off. (Note that the eigenvalues are the singular values squared, so DmrgJanitor::eps_noise must be chosen accordingly).
RICH_SVD	Uses an enrichment scheme, a.k.a. the "Strictly Single-Site (SSS) algorithm" according to Hubig et al. (2015). The matrices are enlarged with non-local information times DmrgJanitor::eps_rsvd, then the usual SVD is performed (using DmrgJanitor::eps_truncWeight as a cutoff parameter). Note that DmrgJanitor::eps_rsvd is a much less sensitive parameter than DmrgJanitor::eps_rdm and can be even kept equal to 1 (but this will result in larger than optimal matrix sizes). Warning Needs Lapack (see above).
QR_NULL	Computes the null space only using full QR decomposition.

Definition at line 261 of file DmrgTypedefs.h.

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The documentation for this struct was generated from the following file:

• DmrgTypedefs.h