slepc-3.22.2 2024-12-02
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# SVDSetDimensions

Sets the number of singular values to compute and the dimension of the subspace.

### Synopsis

    #include "slepcsvd.h"
    PetscErrorCode SVDSetDimensions(SVD svd,PetscInt nsv,PetscInt ncv,PetscInt mpd)

Logically Collective

### Input Parameters

| svd | - the singular value solver context
| nsv | - number of singular values 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

| -svd_nsv <nsv> | - Sets the number of singular values
| -svd_ncv <ncv> | - Sets the dimension of the subspace
| -svd_mpd <mpd> | - Sets the maximum projected dimension

### Notes

Use PETSC_DETERMINE for ncv and mpd to assign a reasonably good value, which is dependent on the solution method and the number of singular values required. For any of the arguments, use PETSC_CURRENT to preserve the current value.

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 nsv is small, the user sets ncv (a reasonable default is 2*nsv); and (b) in cases where nsv is large, the user sets mpd.

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

### See Also

SVDGetDimensions()

### Level

intermediate

### Location

src/svd/interface/svdopts.c

### Examples

src/svd/tutorials/ex8.c
src/svd/tutorials/ex51.c
Index of all SVD routines
Table of Contents for all manual pages
Index of all manual pages