Storing data in matlab matrix using loop

Hello, I am running a loop

i=1;
for k1=2:1:20
    for k2=2:1:20
        for k3 = 2:1:20
        M = [k1,k2,k3];
            if sum(M,'all')==20
               %A = M (matrix containing all three elements, k1,k2,k3) - CODE NEEDED here
            end
        end
    end
end

I want to store all the condition abiding matrices M in matrix A, here, matrix A is the list of all the M matrices.

Thanks.

Answer 1

[Setsuna Yuuki.]

You can try use cell()

i=1;
for k1=2:1:20
    for k2=2:1:20
        for k3 = 2:1:20
        M = [k1,k2,k3];
            if sum(M,'all')==20
              A{i} = M;
               i=i+1;
            end
        end
    end
end 

A{1}
ans =
     2     2    16
     
A{2}
ans =
     2     3    15

Answer 2

[Walter Roberson]

[K1, K2, K3] = ndgrid(2:1:20, 2:1:20, 2:1:20);
M = K1 + K2 + K3;
mask = M == 20;
A = [K1(mask), K2(mask), K3(mask)];
size(A)

ans = 1×2

120 3

By the way: there is no point going as high as 20 in the vectors. You want a sum of 20 and the mininum value for each is 2, so the maximum that it is possible for any valid entry to be is 20 - 2 - 2 = 16, so you might as well only do 2:16