# QEPSetWhichEigenpairs

Specifies which portion of the spectrum is to be sought.

### Synopsis

    #include "slepcqep.h"
    PetscErrorCode QEPSetWhichEigenpairs(QEP qep,QEPWhich which)

Logically Collective on QEP

### Input Parameters

| qep | - eigensolver context obtained from QEPCreate()
| which | - the portion of the spectrum to be sought

### Possible values

The parameter 'which' can have one of these values

| QEP_LARGEST_MAGNITUDE | - largest eigenvalues in magnitude (default)
| QEP_SMALLEST_MAGNITUDE | - smallest eigenvalues in magnitude
| QEP_LARGEST_REAL | - largest real parts
| QEP_SMALLEST_REAL | - smallest real parts
| QEP_LARGEST_IMAGINARY | - largest imaginary parts
| QEP_SMALLEST_IMAGINARY | - smallest imaginary parts
| QEP_TARGET_MAGNITUDE | - eigenvalues closest to the target (in magnitude)
| QEP_TARGET_REAL | - eigenvalues with real part closest to target
| QEP_TARGET_IMAGINARY | - eigenvalues with imaginary part closest to target

### Options Database Keys

| -qep_largest_magnitude | - Sets largest eigenvalues in magnitude
| -qep_smallest_magnitude | - Sets smallest eigenvalues in magnitude
| -qep_largest_real | - Sets largest real parts
| -qep_smallest_real | - Sets smallest real parts
| -qep_largest_imaginary | - Sets largest imaginary parts
| -qep_smallest_imaginary | - Sets smallest imaginary parts
| -qep_target_magnitude | - Sets eigenvalues closest to target
| -qep_target_real | - Sets real parts closest to target
| -qep_target_imaginary | - Sets imaginary parts closest to target

### Notes

Not all eigensolvers implemented in QEP account for all the possible values stated above. If SLEPc is compiled for real numbers QEP_LARGEST_IMAGINARY and QEP_SMALLEST_IMAGINARY use the absolute value of the imaginary part for eigenvalue selection.

### See Also

QEPGetWhichEigenpairs(), QEPWhich

Location: src/qep/interface/qepopts.c
Index of all QEP routines
Table of Contents for all manual pages
Index of all manual pages