Gecode::Search::Options Class Reference
[Search engines]

Search engine options More...

#include <search.hh>

Public Member Functions
	Options (void)
	Initialize with default values.
Options	expand (void) const
	Expand with real number of threads.
Public Attributes
bool	clone
	Whether engines create a clone when being initialized.
double	threads
	Number of threads to use.
unsigned int	c_d
	Create a clone after every c_d commits (commit distance).
unsigned int	a_d
	Create a clone during recomputation if distance is greater than a_d (adaptive distance).
unsigned int	nogoods_limit
	Depth limit for extraction of no-goods.
Stop *	stop
	Stop object for stopping search.
Cutoff *	cutoff
	Cutoff for restart-based search.
Static Public Attributes
static const Options	def
	Default options.

Detailed Description

Search engine options

Defines options for search engines. Not all search engines might honor all option values.

c_d as minimal recomputation distance: this guarantees that a path between two nodes in the search tree for which copies are stored has at least length c_d. That is, in order to recompute a node in the search tree, c_d recomputation steps are needed. The minimal recomputation distance yields a guarantee on saving memory compared to full copying: it stores c_d times less nodes than full copying.
a_d as adaptive recomputation distance: when a node needs to be recomputed and the path is longer than a_d, an intermediate copy is created (approximately in the middle of the path) to speed up future recomputation. Note that small values of a_d can increase the memory consumption considerably.

Full copying corresponds to a maximal recomputation distance c_d of 1.

All recomputation performed is based on batch recomputation: batch recomputation performs propagation only once for an entire path used in recomputation.

The number of threads to be used is controlled by a double $n$ (assume that $m$ is the number of processing units available). If $1 \leq n$ , $n$ threads are chosen (of course with rounding). If $n \leq -1$ , then $m + n$ threads are chosen (all but $-n$ processing units get a thread). If $n$ is zero, $m$ threads are chosen. If $0<n<1$ , $n \times m$ threads are chosen. If $-1 <n<0$ , $(1+n)\times m$ threads are chosen.