Silly mistakes

[eligolf]

I was playing my bot a few games and found that it really played strange in endgames and not what I was expecting it to do. For example it kept its king near g1/g8 which made me think that it was something wrong with how I went from opening to endgame in my PST. Sure enough, I had written my eval as follows:

Code: Select all

// Calculate the current phase
int gamePhaseOpening = Math.Max(boardState.CurrentGamePhase, EvaluationConstants.phaseResolution);
int gamePhaseEnding = EvaluationConstants.phaseResolution - gamePhaseOpening;

// Calculate the scores from PST tables (white minus black score)
int scoreOpening = boardState.PSTValues[Color.White][GamePhase.Opening] - boardState.PSTValues[Color.Black][GamePhase.Opening];
int scoreEnding = boardState.PSTValues[Color.White][GamePhase.Ending] - boardState.PSTValues[Color.Black][GamePhase.Ending];

// Tapered evaluation (https://www.chessprogramming.org/Tapered_Eval)
int score = ((scoreOpening * gamePhaseOpening) + (scoreEnding * gamePhaseEnding)) / EvaluationConstants.phaseResolution;

First row I accidentally set Math.Max instead of Math.Min which made the opening phase always be maximum value and it never went into endgame. After a quick change it was now playing decent endgames, or at least as I expected it to from the endgame tables

Such small mistake that leads to massive decrease in strength... At least this mistake was fairly simple to find

Do you have any examples of small or hard-to-find mistakes which lead to large consequences?