slepc-3.17.0 2022-03-31
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# STSetMatMode

Sets a flag to indicate how the transformed matrices are being stored in the spectral transformations.

### Synopsis

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

Logically 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', 'shell' (see explanation below).

### Notes

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

With ST_MATMODE_INPLACE, the original matrix A is modified at STSetUp() and changes are reverted at the end of the computations. With respect to the previous one, this mode avoids a copy of matrix A. However, a drawback 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 iterative solvers with Jacobi preconditioning can be used).

In the two first modes the efficiency of the computation can be controlled with STSetMatStructure().

### See Also

STSetMatrices(), STSetMatStructure(), STGetMatMode(), STMatMode

Location: src/sys/classes/st/interface/stset.c

### Examples

src/pep/tutorials/ex28.c.html
Index of all ST routines
Table of Contents for all manual pages
Index of all manual pages