STSetMatMode

Sets a flag to indicate how the matrix is being shifted in the shift-and-invert and Cayley spectral transformations.

Synopsis

#include "slepcst.h" 
PetscErrorCode STSetMatMode(ST st,STMatMode mode)
Collective on ST

Input Parameters

st - the spectral transformation context
mode - the mode flag, one of ST_MATMODE_COPY, ST_MATMODE_INPLACE or ST_MATMODE_SHELL

Options Database Key

-st_matmode <mode> - Indicates the mode flag, where <mode> is one of 'copy', 'inplace' or 'shell' (see explanation below).

Notes

By default (ST_MATMODE_COPY), a copy of matrix A is made and then this copy is shifted explicitly, e.g. A <- (A - s B).

With ST_MATMODE_INPLACE, the original matrix A is shifted at STSetUp() and unshifted at the end of the computations. With respect to the previous one, this mode avoids a copy of matrix A. However, a backdraw is that the recovered matrix might be slightly different from the original one (due to roundoff).

With ST_MATMODE_SHELL, the solver works with an implicit shell matrix that represents the shifted matrix. This mode is the most efficient in creating the shifted matrix but it places serious limitations to the linear solves performed in each iteration of the eigensolver (typically, only interative solvers with Jacobi preconditioning can be used).

In the case of generalized problems, in the two first modes the matrix A - s B has to be computed explicitly. The efficiency of this computation can be controlled with STSetMatStructure().

See Also

STSetOperators(), STSetMatStructure(), STGetMatMode(), STMatMode

Location: src/st/interface/stset.c
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Index of all manual pages