[gnugo-devel] a capturing race

[Douglas Ridgway]

In the SGF below, here's the position before move 207:

showboard
=
   A B C D E F G H J K L M N O P Q R S T
19 . . . O X . . . . . . . . . . X . . . 19
18 . . . O X O . . . . . . X . O X O . . 18
17 . X X X O O O . . X X X O O O X O . . 17
16 . . O X X X O . . O X O O X O X . O . 16
15 . . O . O O . O O X . X X X O X X O . 15
14 . O . O . X O O X . X . X O X X O O . 14
13 . X O . O . X X X X . X X O O O O X O 13
12 . X O . . X . . . . X O O O O X X X . 12
11 . O . O . . . . . . X X X O X X X X X 11    
10 . O . O . . . X . X . . X O X O . X . 10    
 9 . X O O . . . . . . . O X X O . O . . 9
 8 X . X X O . X . . . X X O O O O X X X 8
 7 . X . . . . . . X . X O O O O X . . . 7
 6 . X O O O . . X O O O . . . O X . . . 6
 5 . . X X O . . X X X X O O O O X . . . 5
 4 . . . X O . . X O O O X X . O + X . . 4
 3 . . . X O . O O . O X . . X O O X . . 3
 2 . . . . X X . . . O X . X . O X X . . 2
 1 . . . . . . . . . . . . . . . . . . . 1
   A B C D E F G H J K L M N O P Q R S T

In the game, White plays to R19 as a forcing move before returning to the 
capturing race underway at the bottom. GnuGo as Black ignores this, 
tries to save the group at the bottom, and ends up losing both. (This is 
3.4, but the current version has a similar idea.)

I think there are two mistakes here. The main one is misreading the
capturing race at the bottom. But even aside from that, it doesn't seem 
wise for Black to go for a big exchange when a) Black is ahead and b) the 
profit side is uncertain. It seems like this mistake could be avoided even 
without fully understanding the capturing race.

And finally, on the subject of the capturing race, what does it mean for
dragon_status to be critical if one of the moves is PASS? This from a few 
moves later:

showboard
=
   A B C D E F G H J K L M N O P Q R S T
19 . . . O X . . . . . . . . . . X O . . 19
18 . . . O X O . . . . . . X . O X O . . 18
17 . X X X O O O . . X X X O O O X O . . 17
16 . . O X X X O . . O X O O X O X O O . 16
15 . . O . O O . O O X . X X X O X X O . 15
14 . O . O . X O O X . X . X O X X O O . 14
13 . X O . O . X X X X . X X O O O O X O 13
12 . X O . . X . . . . X O O O O X X X . 12
11 . O . O . . . . . . X X X O X X X X X 11    
10 . O . O . . . X . X . . X O X O . X . 10   
 9 . X O O . . . . . . . O X X O . O . . 9
 8 X . X X O . X . . . X X O O O O X X X 8
 7 . X . . . . . . X . X O O O O X . . . 7
 6 . X O O O . . X O O O . . . O X . . . 6
 5 . . X X O . . X X X X O O O O X . . . 5
 4 . . . X O . . X O O O X X . O + X . . 4
 3 . . . X O . O O . O X . X X O O X . . 3
 2 . . . . X X . . . O X . X . O X X . . 2
 1 . . . . . . . . . . X . O O X . . . . 1
   A B C D E F G H J K L M N O P Q R S T

dragon_status m4
= critical M1 PASS

Thanks for any help,

doug.
address@hidden


(;FF[1]GM[1]SZ[19]
AB[dd][dp][pd];W[pq];B[po];W[cn];B[qq];W[op];B[qp];W[oo]
;B[cl];W[eo];B[ci];W[ep];B[dq];W[eq];B[pm];W[df];
B[fd];W[cd];B[cc];W[ce];B[bc];W[ch];B[jc];W[di];B[cj]
;W[dj];B[bh];W[cg];B[er];W[ck];B[bk];W[dk];B[dl];
W[el];B[bg];W[bl];B[fr];W[bf];B[bm];W[bj];B[al];W[bi]
;B[do];W[dn];B[bn];W[qf];B[co];W[en];B[nd];W[rd];
B[qh];W[qc];B[qe];W[re];B[pf];W[qg];B[pc];W[pg];B[ph]
;W[og];B[ff];W[ni];B[pk];W[jq];B[je];W[qb];B[pb];
W[ee];B[ed];W[fe];B[ge];W[gf];B[gg];W[hf];B[fh];W[he]
;B[hg];W[gd];B[hj];W[gc];B[nk];W[eg];B[mg];W[jf];
B[if];W[ie];B[ig];W[jd];B[kc];W[ke];B[me];W[db];B[eb]
;W[ec];B[dc];W[fc];B[ea];W[lh];B[jj];W[oe];B[im];
W[ld];B[lc];W[md];B[ne];W[mc];B[of];W[ng];B[le];W[nf]
;B[kd];W[nc];B[lg];W[ob];B[pa];W[od];B[pe];W[oc];
B[mb];W[lf];B[mf];W[kg];B[kf];W[mh];B[je];W[fb];B[jg]
;W[da];B[kh];W[pj];B[oj];W[pi];B[oi];W[oh];B[rh];
W[qj];B[rg];W[rf];B[rj];W[qk];B[ql];W[rk];B[si];W[sk]
;B[rl];W[sj];B[ri];W[sg];B[mn];W[ol];B[sl];W[ok];
B[qi];W[nj];B[mk];W[om];B[ko];W[kp];B[nn];W[on];B[mp]
;W[pl];B[pn];W[pj];B[pi];W[qk];B[pr];W[lk];B[mj];
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;B[kl];W[kn];B[jo];W[lo];B[ln];W[mo];B[km];W[no];
B[lp];W[jn];B[kq];W[jp];B[io];W[in];B[hn];W[nm];B[hp]
;W[hq];B[kr];W[ip];B[ho];W[gq];B[gl];W[or];B[mr];
W[jr];B[nq];W[oq];B[qr];W[qa];B[jm];W[qd];B[rk];W[nr]
;B[ls];W[lq];B[hb];W[ic];B[ib];W[gr];B[nb];W[oa];
B[id];W[fk];B[fj];W[gk];B[hk];W[gj];B[gi];W[ej];B[fi]
;W[fl];B[gm];W[fq];B[hc];W[fg];B[hd];W[ef];B[gb];
W[fa];B[fn];W[fm];B[fo];W[fs];B[dr];W[np];B[ln];W[mq]
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B[gs];W[hs];B[ma];W[ia];B[ja];W[gp];B[os];W[ns];B[ps]
;W[go];B[gn];W[aj];B[eh];W[dm];B[dh];W[fs];B[sf];
W[se];B[gs];W[kn];B[jn];W[fs];B[sh];W[gs];B[sf];W[nn]
;B[kn];W[sg];B[qj];W[pk];B[sf];W[cm];B[bl];W[sg];
B[pp];W[sf];B[dg];W[ei];B[fp];W[ak];
)