Matrix BILU Threshold#

Matrix BILU threshold = <float>

Description / Usage#

This capability is only present within the Trilinos library. This optional card provides a means to modify the way the block ILU preconditioner (Matrix subdomain solver = bilu) is constructed. The input parameter is defined as:


t, a floating point number ( t ≥ 0.0 ) that sets the Matrix Relative Threshold and Matrix Absolute Threshold thresholds.

When the Matrix BILU threshold card is omitted, the default value is 0.0.


Following is a sample card:

Matrix BILU Threshold = 1.0e-14

Technical Discussion#

Using this card is equivalent to supplying both the Matrix Relative Threshold and Matrix Absolute Threshold with the value specified with this card.

The value of t defaults to zero, and if given a small value, say 1.0e-14, the condition number of the preconditioner, as reported when using the bilu option, should decrease. Try increasing up to around 1.0e-3 to get added benefit. The bilu preconditioner is not actually the cheapest or most efficient preconditioner, but it is very robust.