Markian Hlynka
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Markian Hlynka [1] Markian Hlynka,
a Canadian computer scientist and systems analyst at University of Alberta. Along with Jonathan Schaeffer et al., Markian Hlynka researched and published on search enhancements and temporal difference learning.
Abstract
This paper introduces the idea of pre-searching a position — searching it before [αβ](Alpha-Beta "Alpha-Beta") determines that it needs to be searched. Consider the case where an iteration of αβ search comes across a position p that needs to be searched to [depth](Depth "Depth") d1, and the [transposition table](Transposition_Table "Transposition Table") reveals that p will likely need to be searched later in that iteration to depth d2 greater than d1. Pre-searching involves speculatively searching p to depth d2, even though it has not been demonstrated that search to this depth is needed. If the gamble is successful, then additional accuracy is introduced to the search (using a result with extra search depth d2 − d1). While any search extension scheme is not without some risk, empirical results indicate that the impact on the αβ search tree size is small, but the additional accuracy that is introduced improves program performance.
Pseudo Code
// Assumptions:
// * search depth counts down to 0 (leaf node)
// * IDDepth is the iterative deepening search depth
// * searches are to a fixed depth
int AlphaBeta( state, depth, alpha, beta, presearch ) {
if( TerminalNode( state ) || depth == 0 )
return( Evaluate( state ) );
save_alpha = alpha;
save_beta = beta;
tt_found = TTLook( state, &tt_depth, &tt_value, &tt_bound, &tt_iteration );
if( tt_found == TRUE && tt_depth >= depth ) {
if( tt_bound == LOWER ) alpha = MAX( alpha, tt_score );
if( tt_bound == UPPER ) beta = MIN( beta, tt_score );
if( tt_bound == ACCURATE ) alpha = beta = tt_bound;
if( alpha >= beta ) return( alpha );
}
// Check for pre-search conditions
if( tt_found && // node is in TT
tt_iteration != IDDepth && // not updated this iteration
// Check that entry has deeper search needs
tt_depth + ( IDDepth - tt_iteration) >= depth ) {
// Found a shallow node
new_depth = tt_depth + ( IDDepth - tt_iteration );
if( presearchFilter( newdepth, depth, tt_depth, tt_iteration, presearch ) ) {
presearch = true;
depth = new_depth;
}
}
score = -INFINITY;
num_moves = Generate( state, moves[] );
for( i = 1; i <= num_moves; i++ ) {
result = -AlphaBeta( state.moves[i], depth-1, -beta, -alpha, presearch );
score = MAX( score, result );
alpha = MAX( alpha, score );
if( alpha >= beta )
break;
}
// Normal TT update, but need to also save IDDepth
TTUpdate( state, score, save_alpha, save_beta, depth, IDDepth );
return( score );
}
bool presearchFilter( new_depth, depth, tt_depth, tt_iteration, presearch ) {
// Do not allow a pre-search in a pre-search
if( presearch ) return( false);
// Ensure that we are searching deeper
if( new_depth <= depth ) return( false );
// Limit the amount of the search extension
if( new_depth - depth > Risk ) return( false );
// Prefer deep nodes close to the root
if( tt_iteration - tt_depth > NearRoot ) return( false );
// Prefer shallow nodes that are not close to the leaves
if( depth < NearLeaf ) return( false );
// Pre-search
return( true );
}
Fotos
10th Computer Olympiad,
Go 9x9,
Taipei 2005,
Shih-Chieh Huang and Markian Hlynka operating
Go Intellect and
NeuroGo,
Fredrik Niemelä watching [3]
Selected Publications
- Jonathan Schaeffer, Markian Hlynka, Vili Jussila (2001). Temporal Difference Learning Applied to a High-Performance Game-Playing Program. CGW@IJCAI 2001
- Markian Hlynka, Jonathan Schaeffer (2004). Pre-Searching. ICGA Journal, Vol. 27, No. 4, pdf
- Markian Hlynka, Jonathan Schaeffer (2005). Automatic Generation of Search Engines. Advances in Computer Games 11
External Links
References
- ↑ Photo Gallery: Friends and Peers by Darse Billings
- ↑ Markian Hlynka, Jonathan Schaeffer (2004). Pre-Searching. ICGA Journal, Vol. 27, No. 4
- ↑ CO 10 and ACG 11, Pictures 09/04/2005
- ↑ dblp: Markian Hlynka
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