Tech mate

I am sure I have posed more questions to the chess engine Stockfish than to any living being. I love the instant gratification: you give it a chess position and it gives you an answer: the best move and an evaluation measured in hundredths of a pawn, like +1 24. Leave it alone, it will delve deeper; move a piece, it will respond anew. In human terms, ‘Ooh, a smidgen better for White’ gives way to ‘Go there, and your rook gets blown away’. The chess engine is, by turns, a spirit level and a hurricane forecast.

The basic design of a traditional chess engine like Stockfish is simple: check all the moves, back and forth, for both sides, and tot up the value of the pieces in each scenario. Then choose a move accordingly. But the tree of possibilities is so vast, even for a computer, that you must prune it judiciously: ignore the moves that blunder a queen, but not the brilliant sacrifices that lead to checkmate.