Create Spiral Matrix Matlab - matlab

Question

Can any one help creating spiral matrix in matlab using only loops and if else conditions.
For example n=5, spiral matrix is:
17 16 15 14 13
18 5 4 3 12
19 6 1 2 11
20 7 8 9 10
21 22 23 24 25

Answer 1

There is a function spiral in your MATLAB installation, doing exactly what you want.
>> spiral(5)
ans =
21 22 23 24 25
20 7 8 9 10
19 6 1 2 11
18 5 4 3 12
17 16 15 14 13
You can view the source code typing edit spiral

Answer 2

Try this:
nn = input('');
n = floor(1+(nn)/2);
a = zeros(nn,nn);
i=n;j=n;m=1;br=true;
if rem(nn,2)==0
j=n-1;
nn=nn+2;
end
for p=1:2:nn
k=0;
while k<p-2
k=k+1;
a(i,j)=m;
i=i-1;
m=m+1;
end
k=0;
while k<p-1
k=k+1;
a(i,j)=m;
j=j-1;
m=m+1;
end
k=0;
while k<p-1
if j<1
br = false;
break
end
k=k+1;
a(i,j)=m;
i=i+1;
m=m+1;
end
if ~br
break
end
k=0;
while k<p
k=k+1;
a(i,j)=m;
j=j+1;
m=m+1;
end
end
disp(a)
Here is a sample run:
Enter the number:
5
17 16 15 14 13
18 5 4 3 12
19 6 1 2 11
20 7 8 9 10
21 22 23 24 25
Another one, this time using an even number:
Enter the number:
6
36 35 34 33 32 31
17 16 15 14 13 30
18 5 4 3 12 29
19 6 1 2 11 28
20 7 8 9 10 27
21 22 23 24 25 26
Explanation: It starts with the central cell in the case of an odd number as input, and the bottom-left central cell in the case of an even input. It then, starting with 1 as the value and taking one circulation at a time, moves outwards, traverses right, up, left, down, and right again, incrementing the value to be assigned with each step, until the entire matrix is full.

Answer 3

Here is a custom function SpiralMatrix to construct the spiral matrix as your requested
function M = SpiralMatrix(n)
M = zeros(n);
% start from element M(1,1)
i = 1;
j = 1;
s = 1; % first element assigned to M(1,1)
M(i,j) = s;
while true
% fill row from left to right
idx = find(M(i,:)==0,1,'last');
M(i,j:idx) = s + (0:(idx-j));
s = s + idx - j;
j = idx;
% fill column from top to bottom
idx = find(M(:,j)==0,1,'last');
M(i:idx,j) = s + (0:(idx-i));
s = s + idx - i;
i = idx;
% fill row from right to left
idx = find(M(i,:)==0,1,'first');
M(i,j:-1:idx) = s + (0:(j-idx));
s = s + j - idx;
j = idx;
% fill column from bottom to top
idx = find(M(:,j)==0,1,'first');
M(i:-1:idx,j) = s + (0:(i-idx));
s = s + i-idx;
i = idx;
% break if matrix if fully filled
if nnz(M) == n^2
break;
end
end
M = n^2+1-fliplr(flipud(M));
end
such that
>> SpiralMatrix(5)
ans =
17 16 15 14 13
18 5 4 3 12
19 6 1 2 11
20 7 8 9 10
21 22 23 24 25
>> SpiralMatrix(7)
ans =
37 36 35 34 33 32 31
38 17 16 15 14 13 30
39 18 5 4 3 12 29
40 19 6 1 2 11 28
41 20 7 8 9 10 27
42 21 22 23 24 25 26
43 44 45 46 47 48 49