🚀 go-pugleaf

Here are some observations on pl68 and a few questions:

It seems that pl68 runs slower for a given depth of evaluation than did pl65.
At a depth of 6, I evaluated about 1000 positions on a Sparc IPX with pl65.
Typical run times were about 4 min per position with about 8500 nodes/s.
With pl68, run times are averaging 16 min per postion with about 7000 nodes/s.
These are all positions from openings and early middlegames from ECO's, etc.,
with no particular theme (other than their appeal to me -- a way-below-average
player :) This wasn't intended to be a rigorous test, or even a *test*, I'm
just trying to understand some (!) and (?) lines.

Now, pl68 finds and evaluates draws (especially repetiton of position)
correctly, where pl65 did not.  This is great -- I was about to post some
drawing lines that earlier gnuchess pl's, didn't score correctly.

Now I'm wondering about several concepts dealing with draws:
(1) Bob Hyatt's program Cray Blitz uses the ply distance to draw as bonus
    in the evaluation, with a 100 point "free window" around draw score.
    100 points = 0.1 pawn in Cray Blitz, I think.
It looks like gnuchess does something similar, but it also seems to score
a materially and positionally balanced game with a score of zero, also.
Is there an advantage to having a drawing window like Cray Blitz?
Sometimes in a long sequence of half-pawn advantage or disadvantage lines
there's a zero score in pl68.  Not 1, or 2 or 5 or 6 but 0 and as far as I
can tell there's no draw there!
Surely there's some difference between a known draw and a balanced game...

(2) Steven Edwards posted a note about parallelizing a chess program by using
    a second processor to compute forced checkmate lines.  The idea was that
    a separate evaluation for checkmate could be run more efficiently than
    building that into the general solver.
Is there a similar routine that could be used to find forced draws?

(3) Are there many drawing sequences where pieces just shuffle around and
    achieve three repetitions of position (wait-- three repetitions or THE
    THIRD REPETITION-- whatever!)?
Maybe evaluating all of these "shuffling draws" is slowing down the evaluation
in pl68 -- not a bad thing if one wants draws to be correctly evaluated.

Thanks!


Mike