BVTensorCompress#
Updates the U and S factors of the tensor basis vectors object V by means of an SVD, removing redundant information.
Synopsis#
#include "slepcbv.h"
PetscErrorCode BVTensorCompress(BV V,PetscInt newc)
Collective
Input Parameters#
V - the tensor basis vectors context
newc - additional columns to be locked
Notes#
This function is typically used when restarting Krylov solvers. Truncating a tensor BV V = (I otimes U) S to its leading columns amounts to keeping the leading columns of S. However, to effectively reduce the size of the decomposition, it is necessary to compress it in a way that fewer columns of U are employed. This can be achieved by means of an update that involves the SVD of the low-rank matrix [S_0 S_1 … S_{d-1}], where S_i are the pieces of S.
If newc is nonzero, then newc columns are added to the leading columns of V. This means that the corresponding columns of the U and S factors will remain invariant in subsequent operations.
See Also#
BVCreateTensor(), BVSetActiveColumns()
Level#
advanced
Location#
Implementations#
BVTensorCompress_Tensor() in src/sys/classes/bv/impls/tensor/bvtensor.c
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