While loop infinite loop

Question

so my challenge is to make a MxM zeros matrix but with about 15% of those values as 1s.The 'sum' of all those 1s needs to be as close to 15% as it can, while also making it into a global variable for another function, but for some reason it gets stuck in an infinite loop sometimes. Does anyone know why this is happening?

function [ board ] = randomking1( a,b )
clc
global sum
sum = 0; %initalizes sum to zero

kings = ceil(0.15*a*b); %finds number of kings needed for board size

 board = randi([0,1],a,b); %creates game board of random zeros and ones.
                           % ones being the kings on the board.


 for I = 1:a
        for J = 1:b

             if board(I,J) == 1
                     sum = sum + 1;  %this set of for loops counts the
                                     %number of kings on the board
             end

          end
 end


  while sum > kings || sum < kings-1 %if number of kings on the board is greater than
                       %number needed, the number of ones is reduced. 
       for I = 1:a
         for J = 1:b
               if sum

               if  board(I,J) == 1 %if a board value =1

                      board(I,J) = randi([0,1],1) %randomize 0 or 1

                      if board(I,J) == 0 %if the value becomes zero, subtract from the sum
                   sum = sum - 1
                      end
               end

           end
         end

       end

  disp(sum)
end

"sometimes"? which loop exactly? for which input parameters does it get stuck? — m.s.
– m.s., Commented Apr 19, 2015 at 7:58
Well sometimes it works and gives me the answer i am looking for, but every once and a while it just infinitely outputs 0 after 0 after 0 vertically. I think the problem might be in the while loop. If i enter randomking1(4,4) it outputs a 3 or a 4. If i enter randomking1(5,5) it outputs a 4 or a 5. But for all of these inputs, randomly it will get stuck in the loop, sometimes the first time i enter it, sometimes the fifth time i run it. — kaygoo
– kaygoo, Commented Apr 19, 2015 at 8:05
It does seem to get stuck more often with the higher number matrices that I enter. — kaygoo
– kaygoo, Commented Apr 19, 2015 at 8:16

m.s. · Accepted Answer · 2015-04-19 08:46:18Z

2

Instead of trying to find a solution using your bruteforce method, I suggest placing 15 % kings on the board and then randomizing it.

function [ board ] = randomking1( a,b )

board_size = a*b;
% finds number of kings needed for board size
kings = ceil(0.15*board_size); 

% creates game board (as a linear vector) of ones and zeros
% ones being the kings on the board.
board = [ones(1,kings), zeros(1, board_size-kings)];

% shuffle the board
board = board(randperm(board_size));

% create the a x b matrix out of the linear vector
board = reshape(board,[a,b]);
end

Example run: randomking1(3,3):

board_size =

     9


kings =

     2


board =

     1     1     0     0     0     0     0     0     0


board =

     0     1     0     0     0     1     0     0     0


board =

     0     0     0
     1     0     0
     0     1     0

edited Apr 19, 2015 at 8:46

answered Apr 19, 2015 at 8:19

m.s.

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1 Comment

kaygoo Over a year ago

Sweet! Thanks you so much this really helps with my project!

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