Provided by: librheolef-dev_7.2-2_amd64 #### NAME

```       ilut - incomplete LU factorization preconditionner (rheolef-7.2)

```

#### SYNOPSIS

```           solver pa = ilut(a);

```

#### DESCRIPTION

```       ilut is a function that returns the dual threshold incomplete LU factorization
preconditionner of its argument as a solver(4). The method is described in

ILUT: a dual threshold incomplete LU factorization,
Numer. Lin. Algebra Appl., 1(4), pp 387-402, 1994.

```

#### OPTIONS

```       During the factorization, two dropping rules are used and ilut supports two options:

drop_tol (float)

Any element whose magnitude is less than some tolerance is dropped. This tolerance is
obtained by multiplying the option tolerance drop_tol by the average magnitude of all
the original elements in the current row. By default, drop_tol is 1000*epsilon where
epsilon is the machine precision associated to the Float_2 type.

fill_factor (integer)

On each row, after elimination, only the n_fillin largest elements in the L part and
the fill largest elements in the U part are kept, in addition to the diagonal
elements. The option fill_factor is used to compute n_fillin: n_fillin =
(nnz*fill_factor)/n + 1 where n is the matrix size and nnz is its total number of non-
zero entires. With fill_factor=1, the incomplete factorization as about the same non-
zero entries as the initial matrix. With fill_factor=n, the factorization is complete,
up to the dropped elements. By default fill_factor=10.

```

#### EXAMPLE

```       int fill_factor = 10; double drop_tol = 1e-12; solver pa = ilut (a, fill_factor,
drop_tol);

```

#### IMPLEMENTATION

```       This documentation has been generated from file linalg/lib/ilut.h

```

#### AUTHOR

```       Pierre  Saramito  <Pierre.Saramito@imag.fr>

```

```       Copyright   (C)  2000-2018  Pierre  Saramito  <Pierre.Saramito@imag.fr> GPLv3+: GNU GPL