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java.lang.Objectorg.apache.commons.math3.linear.IterativeLinearSolver
org.apache.commons.math3.linear.PreconditionedIterativeLinearSolver
org.apache.commons.math3.linear.ConjugateGradient
public class ConjugateGradient
This is an implementation of the conjugate gradient method for
RealLinearOperator
. It follows closely the template by Barrett et al. (1994) (figure 2.5). The linear system at
hand is A · x = b, and the residual is r = b - A · x.
A default stopping criterion is implemented. The iterations stop when || r || ≤ δ || b ||, where b is the right-hand side vector, r the current estimate of the residual, and δ a user-specified tolerance. It should be noted that r is the so-called updated residual, which might differ from the true residual due to rounding-off errors (see e.g. Strakos and Tichy, 2002).
In the present context, an iteration should be understood as one evaluation of the matrix-vector product A · x. The initialization phase therefore counts as one iteration.
Besides standard DimensionMismatchException
, this class might throw
NonPositiveDefiniteOperatorException
if the linear operator or
the preconditioner are not positive definite. In this case, the
ExceptionContext
provides some more information
"operator"
points to the offending linear operator, say L,"vector"
points to the offending vector, say x, such that
xT · L · x < 0.
Field Summary | |
---|---|
static String |
OPERATOR
Key for the exception context. |
static String |
VECTOR
Key for the exception context. |
Constructor Summary | |
---|---|
ConjugateGradient(int maxIterations,
double delta,
boolean check)
Creates a new instance of this class, with default stopping criterion. |
|
ConjugateGradient(IterationManager manager,
double delta,
boolean check)
Creates a new instance of this class, with default stopping criterion and custom iteration manager. |
Method Summary | |
---|---|
boolean |
getCheck()
Returns true if positive-definiteness should be checked for both
matrix and preconditioner. |
RealVector |
solveInPlace(RealLinearOperator a,
RealLinearOperator m,
RealVector b,
RealVector x0)
Returns an estimate of the solution to the linear system A · x = b. |
Methods inherited from class org.apache.commons.math3.linear.PreconditionedIterativeLinearSolver |
---|
checkParameters, solve, solve, solve, solve, solveInPlace |
Methods inherited from class org.apache.commons.math3.linear.IterativeLinearSolver |
---|
checkParameters, getIterationManager |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
---|
public static final String OPERATOR
public static final String VECTOR
Constructor Detail |
---|
public ConjugateGradient(int maxIterations, double delta, boolean check)
maxIterations
- the maximum number of iterationsdelta
- the δ parameter for the default stopping criterioncheck
- true
if positive definiteness of both matrix and
preconditioner should be checkedpublic ConjugateGradient(IterationManager manager, double delta, boolean check) throws NullArgumentException
manager
- the custom iteration managerdelta
- the δ parameter for the default stopping criterioncheck
- true
if positive definiteness of both matrix and
preconditioner should be checked
NullArgumentException
- if manager
is null
Method Detail |
---|
public final boolean getCheck()
true
if positive-definiteness should be checked for both
matrix and preconditioner.
true
if the tests are to be performedpublic RealVector solveInPlace(RealLinearOperator a, RealLinearOperator m, RealVector b, RealVector x0) throws NullArgumentException, NonPositiveDefiniteOperatorException, NonSquareOperatorException, DimensionMismatchException, MaxCountExceededException, NonPositiveDefiniteOperatorException
solveInPlace
in class PreconditionedIterativeLinearSolver
a
- the linear operator A of the systemm
- the preconditioner, M (can be null
)b
- the right-hand side vectorx0
- the initial guess of the solution
x0
(shallow copy) updated with the
solution
NonPositiveDefiniteOperatorException
- if a
or m
is
not positive definite
NullArgumentException
- if one of the parameters is null
NonSquareOperatorException
- if a
or m
is not
square
DimensionMismatchException
- if m
, b
or
x0
have dimensions inconsistent with a
MaxCountExceededException
- at exhaustion of the iteration count,
unless a custom
callback
has been set at construction of the IterationManager
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