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My chess algorithm is based on negamax. The relevant part is:

private double deepEvaluateBoard(Board board, int currentDepth, double alpha, double beta, Move initialMove) {
        if (board.isCheckmate() || board.isDraw() || currentDepth <= 0) {
            this.moveHistorys.put(initialMove, board.getMoveHistory()); // this is not working
            return evaluateBoard(board); // evaluateBoard evaluates from the perspective of color whose turn it is.
        } else {
            double totalPositionValue = -1e40;

            List<Move> allPossibleMoves = board.getAllPossibleMoves();
            for (Move move : allPossibleMoves) {
                board.makeMove(move);
                totalPositionValue = max(-deepEvaluateBoard(board, currentDepth - 1, -beta, -alpha, initialMove), value);
                board.unMakeMove(1);

                alpha = max(alpha, totalPositionValue);
                if (alpha >= beta) {
                    break;
                }
            }

            return totalPositionValue;
        }
    }

It would greatly help debugging if I was be able to access the move sequence that the negamax algorithm bases its evaluation on (where on the decision tree the evaluated value is found).

Currently I am trying to save the move history of the board into a hashmap that is a field of the enclosing class. However, it is not working for some reason, as the produced move sequences are not optimal.

Since developing an intuition for negamax is not very easy, I have ended up on banging my head against the wall on this one for quite some time now. I would much appreciate if someone could point me in the right direction!

K. Raivio
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  • One option would be to create some data structure containing both the evaluation and the move list. Then in your `deepEvaluateBoard()` you can return both a move list and an evaluation. Base case would return an empty move list with the evaluation and the other cases would return the evaluation and move list that were returned for the chosen move with the chosen move appended to the beginning of the move list. – Jimmy H. Maslen Nov 14 '20 at 17:50

0 Answers0