Author: Tony Werten
Date: 02:39:41 01/31/01
Go up one level in this thread
On January 30, 2001 at 21:10:12, Robert Hyatt wrote: >On January 30, 2001 at 17:46:28, Severi Salminen wrote: > >>Hi! >> >>What is the definition of BF and how is it calculated (this has probably been >>discussed N times, but...)? Now I'm calculating like this: >> ______________________ >>BF=(DEPTH-1)|(Nodes/root_move_count) >> >>So it means (DEPTH-1)th root. >> >>Example (from Vincent's position): DEPTH=9 plies, Nodes=2'000'000 and we have 38 >>legal moves in root. >> ____________ >>BF=8|2'000'000/38 = 3.9 >> >>Could this be close to the truth? >> >>Severi > > >There are two terms that are intermixed often: > >1. "branching factor" usually means the average number of branches from a >node, which for chess averages 35-38 (depending on who you believe) for the >whole game. > >2. "effective branching factor" is roughly calculated as you mentioned. IE >nodes for iteration N-1 divided into nodes for iteration N. Or you can use >the time. > >This is really "effective branching factor" because there is _nothing_ that >can reduce the true branching factor other than pure forward pruning, where >some moves are thrown out at each and every ply with no searching of any >kind. IE for Crafty, EBF is roughly 3.0... which is actually impossible >on the surface since alpha/beta reduces the branching factor by roughly >the square root of it. square root of 38 is just over 6, which is a >reasonable branching factor for alpha/beta. To get lower, in the case of >crafty, rather than culling some moves by not searching them at all, I simply >search many of them to a lower than usual depth because of the null-move R >value... > >numbers around 3 are very good IMHO. I only wish mine stayed there all the >time. But it can easily run up to 10 or more in oddball positions where >the move ordering breaks down at deeper depths... Is this only in odd positions or do you notice ebf going up with dept as well ? In my program it seems impossible to keep ebf below 3 if dept becomes bigger than say 12. ( except for endgame positions ) Tony
This page took 0.01 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.