slepc-3.18.1 2022-11-02
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# EPSSetDimensions

Sets the number of eigenvalues to compute and the dimension of the subspace.

### Synopsis

    #include "slepceps.h"
    PetscErrorCode EPSSetDimensions(EPS eps,PetscInt nev,PetscInt ncv,PetscInt mpd)

Logically Collective on eps

### Input Parameters

| eps | - the eigensolver context
| nev | - number of eigenvalues to compute
| ncv | - the maximum dimension of the subspace to be used by the solver
| mpd | - the maximum dimension allowed for the projected problem

### Options Database Keys

| -eps_nev <nev> | - Sets the number of eigenvalues
| -eps_ncv <ncv> | - Sets the dimension of the subspace
| -eps_mpd <mpd> | - Sets the maximum projected dimension

### Notes

Use PETSC_DEFAULT for ncv and mpd to assign a reasonably good value, which is dependent on the solution method.

The parameters ncv and mpd are intimately related, so that the user is advised to set one of them at most. Normal usage is that (a) in cases where nev is small, the user sets ncv (a reasonable default is 2*nev); and (b) in cases where nev is large, the user sets mpd.

The value of ncv should always be between nev and (nev+mpd), typically ncv=nev+mpd. If nev is not too large, mpd=nev is a reasonable choice, otherwise a smaller value should be used.

When computing all eigenvalues in an interval, see EPSSetInterval(), these parameters lose relevance, and tuning must be done with EPSKrylovSchurSetDimensions().

### See Also

EPSGetDimensions(), EPSSetInterval(), EPSKrylovSchurSetDimensions()

### Level

intermediate

### Location

src/eps/interface/epsopts.c

### Examples

src/eps/tutorials/ex30.c.html
src/eps/tutorials/ex43.c.html
Index of all EPS routines
Table of Contents for all manual pages
Index of all manual pages