# How to create a checkerboard matrix without inbuilt function.

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Riley Smith on 12 Sep 2017
Commented: Mendi on 6 Sep 2020
I just want to write this matrix, but want to do it using for loops
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0
James Tursa on 12 Sep 2017
Using the sin function for this would be a sin ...
Cedric on 28 Nov 2017
Edited: Cedric on 28 Nov 2017
I had missed this comment ... ;-)
It's one of the rare cases where using a cos would be a sin too ..
0.5-(-1).^((1:n)+(1:n).')/2
or
a = 1 : n ;
a + a.' == 1

Joseph Cheng on 12 Sep 2017
There are much easier ways to do this than nested for loops, reshape is readily available. if you must do it with for loops you want to start off with the template
for Rind=1:Nrows
for Cind=1:Ncols
Checkerboard(Rind,Cind) = ___;%what condition of Rind and Cind gives you the checker board pattern.
%start with the first row what makes a 1 appear when Rind==1 and Cind=a number.
%then think of the sigificant difference between Rind==1 and Rind==2.....
end
end

ksam K on 25 Nov 2017
%Hope this helps you.
function a = checkerboard(n)
a = zeros(n);
for i = 1:n
for j = 1:n
if (i == j)
a (i, j) = 0;
elseif (mod(j, 2) == 0) && (mod(i,2) == 0)
a(i,j) = 0;
elseif (mod(j, 2) == 0) || (mod(i,2) == 0)
a(i,j) = 1;
end
end
end
end
Nitika Gupta on 2 Jun 2019
thanks

Jan Siegmund on 21 May 2020
For an even sized checkerboard:
rows = 6;
cols = 4;
normal = repmat(eye(2,'logical'),[rows/2 cols/2]);
% or
inverted = repmat(~eye(2,'logical'),[rows/2 cols/2]);

Mendi on 5 Sep 2020
It is more natural to use modulus on meshgrid:
[iX,iY] = meshgrid(1:8,1:8);
Bruno Luong on 5 Sep 2020
One liner variant
mod((1:8)+(1:8)',2)
Mendi on 6 Sep 2020
Yeap. The one liner is better.

Bruno Luong on 5 Sep 2020
Edited: Bruno Luong on 5 Sep 2020
Two more methods
toeplitz(mod(0:7,2))
or for even size
kron(ones(4),[0 1;1 0])