Perft, leaf nodes?

[Luis Babboni]

Please say me where I´m wrong.
I understood that perft results are the number of leaf nodes (nodes that do not have more nodes beyond it, at least with perft number limit).
But I believe I found a position where at least Gaviota and Satana (the only engines I understand how to use to calculate perft) give me a result that is not the same I found "by hand".

This is the position:
7k/4R1pp/8/8/8/8/8/7K w - - 0 1



Perft 2 gives me 73 in both engines (and in mine I´m working in) that is the number of leaf nodes without count the position after Re8++ that is, as far as I understood, a leaf node too.

Thanks!

[Luis Babboni]

SOLVED!
Here is the correct definition of Perft:

Perft is recursive number of legal moves.

Perft for depth 1 is number of legal moves from the given position.
Perft for depth N is sum of legal moves for all positions of Perft N-1.

[cdani]

You can use for example Stockfish or Andscacs to calculate perft, too.

Just put
position fen 7k/4R1pp/8/8/8/8/8/7K w - - 0 1

and then
perft 2

[Ajedrecista]

Hello Luis:

SOLVED!
Here is the correct definition of Perft:

Perft is recursive number of legal moves.

Perft for depth 1 is number of legal moves from the given position.
Perft for depth N is sum of legal moves for all positions of Perft N-1.

Here is, in fact, how JetChess perft counter reports perft(2) of that position:

Code: Select all

  1  Re7-e8           0
  2  Re7-f7           5
  3  Re7*g7           3
  4  Re7-d7           5
  5  Re7-c7           5
  6  Re7-b7           5
  7  Re7-a7           5
  8  Re7-e6           5
  9  Re7-e5           5
 10  Re7-e4           5
 11  Re7-e3           5
 12  Re7-e2           5
 13  Re7-e1           5
 14  Kh1-g1           5
 15  Kh1-g2           5
 16  Kh1-h2           5

Total:               73

Just to complete my post:

Code: Select all

 perft(1) =                        16
 perft(2) =                        73
 perft(3) =                     1,241
 perft(4) =                     5,861
 perft(5) =                   101,487
 perft(6) =                   539,658
 perft(7) =                 9,389,471
 perft(8) =                55,628,133
 perft(9) =               970,934,310
perft(10) =             6,203,290,408
perft(11) =           108,581,645,499
perft(12) =           731,006,640,533
perft(13) =        12,821,244,003,733
perft(14) =        89,335,944,621,556
perft(15) =     1,568,592,660,477,175
perft(16) =    11,198,005,325,037,030
perft(17) =   196,680,381,198,782,558
perft(18) = 1,431,536,409,060,656,547

I hope no typos.

Regards from Spain.

Ajedrecista.

[Luis Babboni]

You can use for example Stockfish or Andscacs to calculate perft, too.

Just put
position fen 7k/4R1pp/8/8/8/8/8/7K w - - 0 1

and then
perft 2

Thanks Daniel, I knew just "setboard" command!


Thanks Jesús!
Yes, I was wrong in the definition of perft.
If there is no ties or checkmates before the number in perft command, both are the same but was not the case.

[brtzsnr]

You can also use zurichess, too: https://godoc.org/bitbucket.org/zurichess/tools/perft

Code: Select all

$ ./perft --fen "7k/4R1pp/8/8/8/8/8/7K w - - 0 1" --max_depth 10
Searching FEN "7k/4R1pp/8/8/8/8/8/7K w - - 0 1"
depth        nodes   captures enpassant castles   promotions eval  KNps   elapsed
-----+------------+----------+---------+---------+----------+-----+------+-------
    1           16          1         0         0          0        1722 9.289µs
    2           73          1         0         0          0        1808 40.381µs
    3         1241         44         0         0          0        5345 232.173µs
    4         5861         99         0         0          0        4758 1.2319ms
    5       101487       2192         0         0          0       17750 5.717569ms
    6       539658       9138         0         0          0       36895 14.627033ms
    7      9389471     176283         0         0          0      194111 48.371719ms
    8     55628133     886521         0         0          0      341662 162.816227ms
    9    970934310   18175344         0         0          0      722655 1.343566224s
   10   6203290408   92877449         0         0    1106664      493569 12.568227604s