Author: Ed Schröder
Date: 08:21:22 10/04/98
Go up one level in this thread
>Werner,
>It looks like you did not really study the article -- you got neither the
>implementation nor the author correct ... :-(
>I think you refer to limited razoring as detailed in my article about
>extended futility pruning. The article even lists ANSI-C source code that
>demonstrates how to use both techniques. In order to simplify the
>subsequent discussion, I quote the code as published in my article below.
Through the years I have experimented with this many times and in many
forms. My conclusion is you gain lots of speed increase resulting in deeper
search. Sofar so good but I also noticed the positional understanding drops
considerable so in the end I dropped the idea. Similar experiences?
- Ed -
>/****************************************************************************/
>
>int search(int alpha, int beta, int depth, int move, node parent) {
>
> node current;
> int extend, fmax, fprune, fscore, score, selective;
>
> /* execute the opponent's move and initialize some local variables */
>
> make_move(parent, move, ¤t);
> fprune = selective = 0;
> score = -INFINITY;
>
> /* determine if and how to extend the search at the current node */
>
> extend = extensions(depth, move, current);
> depth += extend;
>
> /* decide about limited razoring at pre-pre-frontier nodes */
>
> fscore = (mat_balance(current) + razor_margin);
> if (!extend && (depth == PRE_PRE_FRONTIER) && (fscore <= alpha)
> && (opposing_pieces(current) > 3)) depth = PRE_FRONTIER;
>
> /* decide about extended futility pruning at pre-frontier nodes */
>
> fscore = (mat_balance(current) + extd_futil_margin);
> if (!extend && (depth == PRE_FRONTIER) && (fscore <= alpha)) {
> fprune = selective = 1;
> score = fmax = fscore;
> }
>
> /* decide about selective futility pruning at frontier nodes */
>
> fscore = (mat_balance(current) + futil_margin);
> if (!check(move) && (depth == FRONTIER) && (fscore <= alpha)) {
> fprune = selective = 1;
> score = fmax = fscore;
> }
>
> /* ``selective == 1'' and ``--INFINITY < score <= alpha'' hold if
> * the search will be selective at the current node.
> *
> * continue like normal but prune all futile moves if ``fprune == 1''
> */
> ...
>
> for (move = first(current), (move!= 0), move = next(current, move))
> if (!fprune || check(move)
> || (fmax + mat_gain(move) > alpha)) {
>
> ... /* <-- the recursive search call is somewhere here */
> }
> ...
>}
>
>/****************************************************************************/
>
>1. Limited razoring applies at pre-pre-frontier nodes with a remaining
> depth of 3 plies. At these nodes you simply reduce the depth by 1 ply
> if the according conditions are fulfilled. Yet you do *not* stop the
> search by returning some fishy score ... where did you get this from?
>
>2. Extended futility pruning applies at pre-frontier nodes with a remaining
> depth of 2 plies. At these nodes you only follow promising captures and
> all checking moves if the according conditions are fulfilled (similar to
> normal/selective futility pruning at frontier nodes). Again, you do *not*
> stop the search immediately but you rather prune unpromising captures
> and all quiet moves based on a static decision at the current node.
>
>=Ernst=
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