# Matrix Auxiliary Vector#

Matrix auxiliary vector = {resid | rand}


## Description / Usage#

This optional card indicates to Aztec how the auxiliary vector r is determined. Permissible options are:

resid

The auxiliary vector is set to the initial residual vector, viz. $$r = r(0)$$.

rand

The auxiliary vector is filled with random numbers, each in the range $$[-1,1]$$.

If the Matrix auxiliary vector card is omitted, the default is resid.

## Examples#

Following is a sample card:

Matrix auxiliary vector = rand


## Technical Discussion#

The auxiliary vector is only used for certain iterative linear matrix solution algorithms.

The rand option may cause difficulties with initial iterative solver steps because different processors may have different initial unknown values at shared unknowns.