How to simulate a random castle in a chessboard?

%the randomly generated castle should be within the chessboard, let say zeros matrix:

CB = zeros (8,8); % chessboard

% and the castle must be the one in this matrix:

C = 1; % Castle

% now randomly generate a castle:

CB (round((8-1)*rand+1),round((8-1)*rand+1))= C; % random generatation for castle

% then i will find out where is the generated castle and i want to generate also randomly a lot of castles, which are not in the same row and column:

[row,column] = find (CB);

x = round((8-1)*rand+1);

y = round((8-1)*rand+1);

I = length (row);

while row(I,:)~= x && row(I,:)~= y && column(I,:)~= y && column(I,:)~= x

CB (x,y)= C;

[row,column] = find (CB);

I = length (row);

x = round((8-1)*rand+1);

y = round((8-1)*rand+1);

end

disp (CB)

the problem is, i dont want to accept any number from row and column in the while loop. I tried with any, all and ismember (functions) but i is not working.

[Giuseppe Inghilterra]

I don' understand well which is your problem.

Firstly, I advise you to use "randi" function, instead of round((8-1)*rand+1) (reference: https://www.mathworks.com/help/matlab/ref/randi.html) . In this way you generate random integer numbers.

Secondly, you could generate two random integer vectors:

x = randi(8,10,1); %this generates a vector of size [10,1] where each entry is within range [1,8].
y = randi(8,10,1);
CB(x,y) = C;

In this way CB matrix has value C=1 in 10 positions defined by pairs (x,y).

But, I don't understand what you want to do, i.e do you want to generate one random pair (x_i,y_i) per time and then if CB(x_i,y_i) is zero then you fill with 1 otherwise you stop while loop?

[Osama Tabbakh]

yes, i want to fill the matrix (zeros) with 1 (one by one), but if one is in a position, the next one should not be in the same column and row.

Answer 1

[Giuseppe Inghilterra]

Hi,

if you try to run this code:

close all
clear all
clc

n = 8;              %chessboard size
CB = zeros(n,n);    %init chessboard
k = 0;
niter = 0;

while(k<n)          %stop condition
    x = randi(n);
    y = randi(n);
    
    if sum(CB(x,:))+sum(CB(:,y)) == 0 
        CB(x,y) = 1;
        k = k+1;
    end
    niter = niter + 1;
end

spy(CB,'ro',28)
hold on
spy(~CB,'b+',28)

you fill with 1 if there are no ones in the same row or column, obtaining following result (this plot changes every time due to introduced randomness with randi function):

Hope this helps.

[Osama Tabbakh]

Thanks, it is working