Author: martin fierz
Date: 15:14:26 03/20/02
Go up one level in this thread
On March 20, 2002 at 15:13:58, Gian-Carlo Pascutto wrote: >In the Dutch championship 2001, my program reached the following >position with black against Rebel Century > >[D]r2q1rk1/pbp1bppp/1p2pn2/8/3P1B2/2PB1N2/PP2QPPP/R4RK1 b - - 0 1 > >It played the losing move a5?, and proceeded with the 'plan' of >pushing it further along the a-file. > >Nowadays, it would find the correct c5 after about a minute >of search, but it is clear by looking at the variations that >it is more due to luck and that it is still not really understanding >what is going on. > >I am wondering if one of the strong players is able to explain >why c5 is good and a5 is not. I would play c5 myself, but I >have to admit I would not be able to explain why it is better >either. I just know it is good to hit at the d4 pawn with the >c pawn if possible, but I suspect there is more to it? the key is pawn structure: after c5, white gets either an isolated quuens pawn (IQP), or he gets abcfgh-abefgh (33-42). both these pawn structures are not just bad in themselves, rather, the evaluation depends heavily on the number and kind of pieces on the board. the IQP generally is bad when many pieces are exchanged and when black controls d5. in this particular position, after a possible c5 cxd4 cxd4, you have exchanged one minor piece, and have d5 firmly controlled. it's surely a bad IQP for white, but not really bad yet (take another pair or two of minors off or so, especially the white squared bishops, and it's really bad). the 33-42 structure is also tricky: with a lot of material on board, it favors the 42 side, because this side can move pawns to e5 and f5 in this example, getting a strong grip on the center + attacking chances against the white king. however, if the heavy pieces disappear, then the 3-2 q-side majority favors the 33 side. if the heavies stay on, the outside majority is not so important, even then, the center control should favor the 4-2 side. the pawn structure without c5 and transformation is simply good for white, because he controls the center. so c5 is a good move in this position, because both the resulting IQP and 42-33 favor black. a5 is really bad move, not only becuase it does nothing, but also because it makes a later c5 less effective, because it weakens black's q-side pawns. as you can see, the whole subject is rather messy, because pawn structure and pieces on the board have to be considered. but if you just do pawn structure alone you are doing something seriously wrong... and these rules here are simple enough to fit into an evaluation. aloha martin
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