Matrix ILUT Fill Factor

Matrix ILUT fill factor = <float>

Description / Usage

This optional card provides a second criterion to Aztec to be used in conjunction with preconditioners based on ILUT approximate factorization, where

<float>

fac, a floating point value ( fac ≥ 0 ) that specifies, very crudely, how many nonzero entries the approximate factorization will contain relative to the number of nonzero entries in the original matrix.

If the Matrix ILUT fill factor card is omitted, the default is 1.

Examples

Following is a sample card:

Matrix ILUT fill factor = 2.0

Technical Discussion

By increasing this factor, the preconditioner becomes more accurate because more terms in the preconditioner (pseudo-inverse) are retained. A value of 1.0 indicates that the preconditioner would contain approximately the same number of nonzero entries as the original matrix.

The two main parameters when using the ILUT preconditioner are this card and the Matrix drop tolerance card. If the Matrix drop tolerance is 0.0, then this card determines the size of the preconditioner. If Matrix drop tolerance is greater than 0.0, then the approximate factorization is first created subject to this card’s restriction, and then the drop tolerance is applied. This can result in a preconditioner with significantly fewer nonzero entries.