Successive Over Relaxation - SOR Method
Background
Suppose that iteration is used to solve the linear system ,
and that is
an approximate solution. We call the
residual vector, and if is
a good approximation then
. A
method based on reducing the norm of the residual will produce a sequence
that converges faster. The successive over relaxation - SOR method introduces a
parameter
which speeds up convergence. The SOR method can be used in the numerical
solution of certain partial differential equations.
Consider that the n�n square matrix A
is split into three parts, the main diagonal D,
below diagonal L and above diagonal
U. We have A
= D - L - U.
=
--
Definition (Diagonally Dominant). The
matrix is
strictly diagonally dominant if
for .
Theorem ( Jacobi
Iteration ). The solution to
the linear system can
be obtained starting with ,
and using iteration scheme
where
and .
If
is carefully chosen a sequence
is generated which converges to the solution P, i.e. .
A sufficient condition for the method to be applicable is that A is
strictly diagonally dominant or diagonally dominant and irreducible.
Theorem ( Gauss-Seidel
Iteration ). The solution to
the linear system can
be obtained starting with ,
and using iteration scheme
where
and .
If
is carefully chosen a sequence
is generated which converges to the solution P, i.e. .
A sufficient condition for the method to be applicable is that A is
strictly diagonally dominant or diagonally dominant and irreducible.
Theorem ( SOR
Iteration ). Given a value of
the parameter (chosen
in the interval
), the
solution to the linear system can
be obtained starting with ,
and using iteration scheme
where
and .
If
is carefully chosen a sequence
is generated which converges to the solution P, i.e. .
Remark. A theorem of Kahan states that the
SOR method will converge only if is
chosen in the interval .
Remark. When we choose the
SOR method reduces to the Gauss-Seidel method.
Mathematica Subroutine (Jacobi Iteration).
Mathematica Subroutine (Gauss-Seidel Iteration).
Mathematica Subroutine (Successive Over Relaxation).
|