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# PEPSetInterval

Defines the computational interval for spectrum slicing.

## Synopsis

    #include "slepcpep.h"
    PetscErrorCode PEPSetInterval(PEP pep,PetscReal inta,PetscReal intb)

Logically Collective

## Input Parameters

- pep - the polynomial eigensolver context

- inta - left end of the interval

- intb - right end of the interval

## Options Database Key

- -pep_interval <a,b> - set \([a,b]\) as the interval of interest

## Notes

Spectrum slicing is a technique employed for computing all eigenvalues of symmetric quadratic eigenproblems in a given interval, see section Spectrum Slicing for PEP. This function provides the interval to be considered. It must be used in combination with `PEP_ALL`, see `PEPSetWhichEigenpairs()`. Note that in polynomial eigenproblems spectrum slicing is implemented in `PEPSTOAR` only.

In the command-line option, two values must be provided. For an open interval, one can give an infinite, e.g., `-pep_interval 1.0,inf` or `-pep_interval -inf,1.0`. An open interval in the programmatic interface can be specified with `PETSC_MAX_REAL` and -`PETSC_MAX_REAL`.

## See Also

PEP: Polynomial Eigenvalue Problems, Spectrum Slicing for PEP, `PEPGetInterval()`, `PEPSetWhichEigenpairs()`, `PEPSTOAR`

## Level

intermediate

## Location

src/pep/interface/pepbasic.c

## Examples

src/pep/tutorials/ex40.c
src/pep/tutorials/ex38.c

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