# QEPComputeResidualNorm

Computes the norm of the residual vector associated with the i-th computed eigenpair.

### Synopsis

    #include "slepcqep.h"
    PetscErrorCode QEPComputeResidualNorm(QEP qep,PetscInt i,PetscReal *norm)

Collective on QEP

### Input Parameter

| qep | - the quadratic eigensolver context
| i | - the solution index

### Output Parameter

norm - the residual norm, computed as ||(l^2*M+l*C+K)x||_2 where l is the eigenvalue and x is the eigenvector. If l=0 then the residual norm is computed as ||Kx||_2.

### Notes

The index i should be a value between 0 and nconv-1 (see QEPGetConverged()). Eigenpairs are indexed according to the ordering criterion established with QEPSetWhichEigenpairs().

### See Also

QEPSolve(), QEPGetConverged(), QEPSetWhichEigenpairs()

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