Description of ILUT

ILUT<Matrix>		Programmers Guide
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Category:itl,functors

Component type:type

Description

The algorithm of ILUT(A, 0, 1.0e-6) is slower than ILU(A). If No fill-in is arrowed , please use ILU instead of ILUT.

  Usage:
    Matrix A;
    int fill_in=5;
    double threshold = 1.0e-5;
    ILUT precond(A, fill_in, threshold);
    qmr(A, x, b, precond.left(), precond.right(), iter);

Matrix has to be unsymmetric. For symmetric one, use incomlete cholesky. Notes: The idea under a concrete Preconditioner such as Incomplete LU is to create a Preconditioner object to use in iterative methods.

Example

In ilut.cc:

typedef matrix< Type, 
                rectangle<>, 
                array< compressed<> >, 
                row_major >::type Matrix;
  Matrix A(5, 5);
  dense1D<Type> x(A.nrows(), Type(0));
  dense1D<Type> b(A.ncols());
  for (dense1D<Type>::iterator i=b.begin(); i!=b.end(); i++)
    *i = 1.;

  // ilut preconditioner
  ILUT<Matrix> precond(A, 0, 1.e-3);

  //iteration
  noisy_iteration<double> iter(b, max_iter, 1.e-6);

  //qmr algorithm
  qmr(A, x, b, precond.left(), precond.right(), iter);

Definition

ilut.h

Template Parameters

Parameter	Description	Default
`Matrix`	Matrix

Model of

Members

Member	Where defined	Description
`Precond`		The preconditioner type
`Left`		The left preconditioner type
`Right`		The right preconditioner type
`ILUT ()`		Default Constructor
`ILUT (const Matrix& A, int k_, double eps_)`		Construct from Matrix A, max fill-ins (k), and threshold (eps)
`void print ()`
`Precond operator() ()`		return a right or Left Preconditioner object
`Left left ()`		return the Left part of a Split Preconditioner object
`Right right ()`		return the Right part of a Split Precondtioner objet

New members

Notes

See also