Othello game, gave up debugging

**Nutshell** · 01-23-2003

Ah well...

Hope you guys can tell me what you think of the game. I gave up debugging it. It plays a bit better than before, but the bug is still there.

***kermi3*** · 01-23-2003

What is the bug?

**Nutshell** · 01-23-2003

Well firstly, the generateMoves() function tend to report wrong figures. It's suppose to return the number of legal moves (mobility), but it doesn't. In the mid-game it reports stuff like 90, 80 etc...where there are only 64 squares on the board.

Secondly the minimax algorithm seems to have a serious implementation problem, even though i took the algorithm pseudocode from a othello game thesis someone made. I had to switch over the min and max evaluation procedures to make it work.

I posted a thread earlier about the bugs, but no one responded. Well, it's ok, no-one's obligued to help me. But now at least tell me what you think of the game >_<.

**Hammer** · 01-24-2003

>>In the mid-game it reports stuff like 90, 80 etc
I haven't looked at the code yet, but are you sure you're not counting somethings twice by mistake, or maybe counting outside of the board?

**Nutshell** · 01-24-2003

Nah, the value jumps suddenly from 5 to like 80 and jumps back down again...

Anywayz, how was the game Hammer? And everyone else?

**RoD** · 01-24-2003

I've been looking at the code, and i have a few ideas. If its not fixed when i get home from school (around 1pm EST) i'll get back on it.

**Nutshell** · 01-24-2003

I've actually fixed some minor bugs since the last time i posted the source at the other thread. This is the most updated version of the code. Note that i've actually swapped the code between MINIMIZE and MAXIMIZE, it seems to play better that way, i think it's the problem of the implementation of minimax, but don't have any idea how to fix it, as i said, i copied the algorithm from a pdf on a site.

**RoD** · 01-24-2003

i dloaded, gimme a few hours.

**PJYelton** · 01-24-2003

Did you get my private message I sent yesterday? I haven't been able to find yet why your generatemoves function isn't working yet, but you have a serious flaw with the implemenation of your minimax.

Minimax ONLY works if a board can only have one value at a given time irregardless of who made the last move. Right now you have it set up so that both player 1 and player 2 are trying to get the highest possible value. So when it is player one's move (which is in mode maximum) he is trying to get the highest possible positive value. But when it is player 2's turn to move, then a great score for him is ALSO positive, yet its mode minimize, so he in turn ends up picking the lowest score - which is bad for him because he wants positive!

What you need to do is change the eval function so that if the board is in favor of player 1 then it has a positive score, and if the board is in favor of player 2 then it it has a negative score - irregardless of who made the last move - ALWAYS. In fact, don't even pass to the eval function the player who made the last move, it shouldn't matter at all to it.

Let me know if this makes sense, and if not I'll try and explain it better!

**PJYelton** · 01-24-2003

Oh, and I think you said you changed this part recently, but make sure you change these lines:

Code:

      if ( mode == MINIMIZE )
         if ( evalVal > max) {
            max = evalVal;
            chosenMove->row = listMoves[ counter ].row;
            chosenMove->col = listMoves[ counter ].col;
         }
      else if ( mode == MAXIMIZE )
         if ( evalVal < min ) {
            min = evalVal;
            chosenMove->row = listMoves[ counter ].row;
            chosenMove->col = listMoves[ counter ].col;
         }

back to

Code:

      if ( mode == MINIMIZE )
         if ( evalVal < min) {
            min = evalVal;
            chosenMove->row = listMoves[ counter ].row;
            chosenMove->col = listMoves[ counter ].col;
         }
      else if ( mode == MAXIMIZE )
         if ( evalVal > max) {
            max = evalVal;
            chosenMove->row = listMoves[ counter ].row;
            chosenMove->col = listMoves[ counter ].col;
         }

I'm pretty sure you minimax was right to begin with, just needed to change the eval function.

**Nutshell** · 01-24-2003

Thanks. But it still doesn't seem total correct after i did this. What i did was change this

Code:

if ( depth <= MAX_DEPTH )
         evalVal = minimax( depth + 1, otherPlayer( player ), boardCopy, &chosenMove );
      else
         evalVal = evalBoard( boardCopy, player );

to....

Code:

if ( depth <= MAX_DEPTH )
         evalVal = -minimax( depth + 1, otherPlayer( player ), boardCopy, &chosenMove );
      else
         evalVal = evalBoard( boardCopy, player );

What about not doing the above and doing this:

Code:

else if ( mode == MAXIMIZE ) {
         evalVal = -evalVal;
         if ( evalVal < min ) {
            min = evalVal;
            chosenMove->row = listMoves[ counter ].row;
            chosenMove->col = listMoves[ counter ].col;
         }
      }

Also, if i change this

Code:

      if ( mode == MINIMIZE )
         if ( evalVal > max) {
            max = evalVal;
            chosenMove->row = listMoves[ counter ].row;
            chosenMove->col = listMoves[ counter ].col;
         }
      else if ( mode == MAXIMIZE )
         if ( evalVal < min ) {
            min = evalVal;
            chosenMove->row = listMoves[ counter ].row;
            chosenMove->col = listMoves[ counter ].col;
         }

back it will play Very bad. See how i mean a frustrating bug. Please give a hand, i realli want to do this well.

**PJYelton** · 01-24-2003

Try this, as far as I can see this should work:

Code:

      if ( mode == MINIMIZE ) {
         evalVal=-evalVal;
         if ( evalVal < min) {
            min = evalVal;
            chosenMove->row = listMoves[ counter ].row;
            chosenMove->col = listMoves[ counter ].col;
         }
      else if ( mode == MAXIMIZE )
         if ( evalVal > max ) {
            max = evalVal;
            chosenMove->row = listMoves[ counter ].row;
            chosenMove->col = listMoves[ counter ].col;
         }

**PJYelton** · 01-24-2003

Ahah! Found another major bug! Make sure you change to what I wrote in the post above and also make sure you change the line

Code:

return evalVal;

at the end of the minimax function to

Code:

if (mode==MAXIMIZE)
  return max;
else
  return min;

You were accidentally sending back the evalVal which will always be the last move the function looked at, NOT the best value! Try this and see how much it helps.

**RoD** · 01-24-2003

i found nothing not already said, sorry.

**PJYelton** · 01-24-2003

Oops, actually I just realized that you can't just make evalVal negative like that. Really you should change the program so that you can get an accurate value from the board without having to know who made the last move so that you know that a negative value is ALWAYS good for player 2 and positive is ALWAYS good for player 1. But if you want to keep it the way you have it, I think you need to first take out the line

Code:

evalVal=-evalVal;

under the if(mode==MINIMIZE). You only want to have it change signs when you actually evaluate the board and never again, so change the line

Code:

if ( depth <= MAX_DEPTH )
         evalVal = minimax( depth + 1, otherPlayer( player ), boardCopy, &chosenMove );
      else
         evalVal = evalBoard( boardCopy, player );

to

Code:

if ( depth <= MAX_DEPTH )
         evalVal = minimax( depth + 1, otherPlayer( player ), boardCopy, &chosenMove );
      else {
         evalVal = evalBoard( boardCopy, player );
         if (mode==MINIMIZE)
              evalVal=-evalVal;
      }

I think this should work. But like I said the standard (and best)way is take out the player parameter in the evalBoard() function.

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