maspack.solvers

Class HybridSolvePolicy

java.lang.Object

maspack.solvers.HybridSolvePolicy

public class HybridSolvePolicy
extends java.lang.Object

Decides when hybrid direct/iterative solves should use an iterative solve (preconditioned by the most recent factorization) and when they should refactor.

Solves are grouped into cycles, each beginning with a direct solve. If t_d is the time of the direct solve and t_1, ... t_n are the times of the following iterative solves, the policy tries to minimize the average solve time

 tavg = (t_d + t_1 + ... + t_n) / (n+1)
 

by requesting a refactor as soon as tavg stops decreasing, i.e., when t_n >= tavg_(n-1). An iterative solve failure also causes a refactor.

If hybrid solves give no benefit in a cycle, because the first iterative solve takes at least as long as the direct solve, or because it fails, the policy backs off by skipping iterative solves for a number of solves. The backoff starts at getInitialBackoff() and doubles for each consecutive unsuccessful cycle, up to getMaxBackoff(). It is cleared when a first iterative solve succeeds.

Times can be given in any units, provided they are consistent.

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_INITIAL_BACKOFF
static int	DEFAULT_MAX_BACKOFF

Constructor Summary

Constructors

Constructor and Description
HybridSolvePolicy()

Method Summary

Modifier and Type	Method and Description
int	getBackoff() Returns the length of the most recent backoff, or 0 if the backoff has been cleared.
double	getCycleAverage() Returns the average solve time for the completed solves in the current cycle, or 0 if there are none.
int	getCycleSolves() Returns the number of completed solves in the current cycle, including the direct solve.
int	getInitialBackoff()
int	getMaxBackoff()
int	getSkipCount() Returns the number of solves remaining in the current backoff.
void	invalidateFactor() Indicates that the current factorization is no longer valid (e.g., because the matrix structure has been reanalyzed), so that the next solve must be direct.
boolean	isRefactorPending() Queries whether a refactor has been requested.
int	numBackoffs()
int	numDirectSolves()
int	numFailedSolves()
int	numIterativeSolves()
void	recordDirect(double time) Records a direct (factor and) solve, which starts a new cycle.
void	recordIterative(double time) Records a successful iterative solve.
void	recordIterativeFailure() Records a failed iterative solve.
void	reset() Resets the policy to its initial state, clearing all timing, cycle and backoff information.
void	setInitialBackoff(int n)
void	setMaxBackoff(int n)
boolean	useIterative() Queries whether the next solve should be iterative.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_INITIAL_BACKOFF

public static final int DEFAULT_INITIAL_BACKOFF

See Also:

Constant Field Values

DEFAULT_MAX_BACKOFF

public static final int DEFAULT_MAX_BACKOFF

See Also:

Constant Field Values

Constructor Detail

HybridSolvePolicy

public HybridSolvePolicy()

Method Detail

reset

public void reset()

Resets the policy to its initial state, clearing all timing, cycle and backoff information. Settings are preserved.

invalidateFactor

public void invalidateFactor()

Indicates that the current factorization is no longer valid (e.g., because the matrix structure has been reanalyzed), so that the next solve must be direct.

useIterative

public boolean useIterative()

Queries whether the next solve should be iterative. Should be called only when an iterative solve is otherwise possible, since a negative answer may count toward a backoff.

Returns:

true if the next solve should be iterative

recordDirect

public void recordDirect(double time)

Records a direct (factor and) solve, which starts a new cycle.

Parameters:

time - time required for the solve

recordIterative

public void recordIterative(double time)

Records a successful iterative solve.

Parameters:

time - time required for the solve

recordIterativeFailure

public void recordIterativeFailure()

Records a failed iterative solve. The caller is expected to follow this with a direct solve. The time spent in the failed solve is not recorded, so that the ensuing direct solve starts a cycle in the same way as when a refactor is requested.

isRefactorPending

public boolean isRefactorPending()

Queries whether a refactor has been requested.

Returns:

true if a refactor is pending

getCycleSolves

public int getCycleSolves()

Returns the number of completed solves in the current cycle, including the direct solve.

Returns:

number of solves in the current cycle

getCycleAverage

public double getCycleAverage()

Returns the average solve time for the completed solves in the current cycle, or 0 if there are none.

Returns:

average solve time for the current cycle

getBackoff

public int getBackoff()

Returns the length of the most recent backoff, or 0 if the backoff has been cleared.

Returns:

current backoff length

getSkipCount

public int getSkipCount()

Returns the number of solves remaining in the current backoff.

Returns:

remaining backoff solves

getInitialBackoff

public int getInitialBackoff()

setInitialBackoff

public void setInitialBackoff(int n)

getMaxBackoff

public int getMaxBackoff()

setMaxBackoff

public void setMaxBackoff(int n)

numDirectSolves

public int numDirectSolves()

numIterativeSolves

public int numIterativeSolves()

numFailedSolves

public int numFailedSolves()

numBackoffs

public int numBackoffs()