MATLAB: How to store a matrix without delete the previous one using a loop

store matrix with a loop

Hi, in my code I´m doing a loop in order to create a 2X4 matrix and the idea is allocate each matrix under the last one, but each time it runs the previous matrix is deleted. my look like this
for i=1:10
  for j=1:10
      nodo1=[i,j];
      nodo2=[i+1,j];
      nodo3=[i,j+1];
      nodo4=[i+1,j+1];
      punto_med=(nodo1+nodo2+nodo3+nodo4)/4;
      distancia=sqrt((5-punto_med(1,1))^2+(5-punto_med(1,2))^2);
      if distancia <=5
          nodos= [nodo1; nodo2; nodo2; nodo3];
          nodos_totales(:,:) = nodos
      end
  end
end
where nodos_totales don´t store all the matrix.
thenk if any one can help me.

Best Answer

Use a 3D array:
c = 0;
for i=1:10
  for j=1:10
    ...
    if distancia <=5
        c = c + 1;
        nodos_totales(:, c) = [nodo1; nodo2; nodo2; nodo3]
    end
Or a cell array:
           nodos_totales{c} = [nodo1; nodo2; nodo2; nodo3]
Note: The SQRT is an expensive operation. Instead of comparing sqrt(x) <= 5 it is much cheaper to compare x < 25.
For this small problem of maximum size 10x10 a pre-allocation is not so important. But it is a good programming practice to pre-allocate in any case:
Before the code:
nodos_totales = zeros(4, 100)
and at the end:
nodos_totales = nodos_totales(:, 1:c);
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