slepc-3.18.0 2022-10-01
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# MatNormEstimate

Estimate the 2-norm of a matrix.

### Synopsis

    #include "slepcsys.h"
    PetscErrorCode MatNormEstimate(Mat A,Vec vrn,Vec w,PetscReal *nrm)

Collective on A

### Input Parameters

| A | - the matrix
| vrn | - random vector with normally distributed entries (can be NULL)
| w | - workspace vector (can be NULL)

### Output Parameter

| nrm | - the norm estimate

### Notes

Does not need access to the matrix entries, just performs a matrix-vector product. Based on work by I. Ipsen and coworkers https://ipsen.math.ncsu.edu/ps/slides_ima.pdf

The input vector vrn must have unit 2-norm. If vrn is NULL, then it is created internally and filled with VecSetRandomNormal().

### See Also

VecSetRandomNormal()

### Level

developer

### Location

src/sys/mat/matutil.c
Index of all sys routines
Table of Contents for all manual pages
Index of all manual pages