storing data in a matrix from a nested loop

I want to save the vector made from d12 each time i.e. d12 is 4*3 matrix. d12 in nested loop

d1 = [0	   0	 2	
      0	   0	-2	];
d2 = [0	   0	 15	
      0	   0	13	];
 for i = 1:2
    for j = 1:2 
        d12() = [d1(i,:)-d2(j,:)];
   end
end

Answer 1

[rajesh regar]

d1 = [0	   0	 2	
      0	   0	-2	];
d2 = [0	   0	 15	
      0	   0	13	];
k = 1;
 for i = 1:2
    for j = 1:2 
        d12(k,:) = [d1(i,:)-d2(j,:)];
        k = k+1;
   end
end

you can initiate k as 1 then increase it by one

[Stephen23]

d12 should be preallocated:

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html

[rajesh regar]

Thank you, it is really helped me

Answer 2

[Stephen23]

No loops required:

>> d1 = [0,0,2;0,0,-2]
d1 =
     0     0     2
     0     0    -2
>> d2 = [0,0,15;0,0,13]
d2 =
     0     0    15
     0     0    13
>> out = repelem(d1,size(d2,1),1) - repmat(d2,size(d1,1),1)
out =
     0     0   -13
     0     0   -11
     0     0   -17
     0     0   -15

This gives exactly the sme output as your nested loops:

>> isequal(out,d12)
ans =
     1

[madhan ravi]

+1 , far more elegant :)

[rajesh regar]

Thank you, I have to use loop for solving my problem because I need to define more variable and finally I will put in formula. Also the size of nested loop in my case is aroung 1000*1000 i.e. need to vary i = 1:1000 and j = 1:1000.

Answer 3

[madhan ravi]

[m,n]=size(d1);
[m1,n1]=size(d2);
z = permute(reshape(d1.',1,n,m) - d2,[2,1,3])
d12 = reshape(z,n,[]).'

% Or if you prefer a loop
k = 1;
d12 = zeros(m+m1,n); % preallocate
 for ii = 1:m % don't hardcode the sizes , use size() instead
    for jj = 1:m1 
        d12(k,:) = d1(ii,:) - d2(jj,:); 
        k = k+1;
   end
end