how can k set the initial variable of my vector

Hello; l set an initial value of a vector to [] neighbour_n= [];but once inside the loop neighbour_n(k)= [neighbour_n(k) j] doesnt work it returns me this message the variable n(i) appears to change size in every loop iteration within the script consider prellocating for speed My target is to get a vector of indices [1 3 5 6 ..] returned error : %

??? Attempted to access neighbour_n(1); index out of bounds because numel(neighbour_n)=0.

Error in ==> agawa at 52
            neighbour_n(k)= [neighbour_n(k) j];
%

my code: %

N=200;
*neighbour_n(k)= [];*
m=0;

for k=1:N;

      for j= k+1 : N;

          d =((nodesX(k)-nodesX(j))^2+(nodesY(k)-nodesY(j))^2)^0.5;

          if d<=200;
              m=m+1; % number of created links
              line([nodesX(k),nodesX(j)],[nodesY(k),nodesY(j)]);
              A(k, j)=1; 

              neighbour_n(k)= [neighbour_n(k) j];
          else
               A(k, j)=0; 
          end;

      end;
  display(A(k, j));
  end;
%

Answer 1

[Geoff Hayes]

mazari - in the line of code

 neighbour_n(k)= [neighbour_n(k) j];

you are trying to access neighbour_n(k) (for k equals one) before it has been created. I think that you are trying to compensate for this with your line of code

 neighbour_n(k)= [];

which isn't quite correct in terms of syntax. As the code only updates the kth row of neighbour_n if the distance condition is met, I suspect that you want neighbour_n to be a cell array as each row can have a different number of columns (neighbours). Try initializing this array outside the for loop as

 neighbour_n = cell(N,1);

and then update the kth row as

 neighbour_n{k}= [neighbour_n{k} j];

Note the use of the curly braces as neighbour_n is a cell array. Try implementing the above and see what happens!

[mazari ahmed]

Thanks Geoff Hayes it works but l experience trouble with this line of code(after neighbour_n{k}= [neighbour_n{k} j]; ). display(['the neighbours of', {k}, 'are', '=' , neighbour_n{k}]);

it doesn't visualize all the neighbours, instead of visualizing for exempple the neighbours of {1} are {3,5,7,2} it visualizes : {1} are {3,[1x2 double],[1x2 double],[1x2 double]}

[Geoff Hayes]

Try converting neighbour_n{k} to a string as

 display(['the neighbours of ', num2str(k), ' are ', ' = ' , num2str(neighbour_n{k})]);

[mazari ahmed]

Thanks Geoff l'm new in this community.l edit it in a another question "how to broadcast a message "hello" to all the neighbors of a node and receive a message "ACK" and how to isolate a node" . l'm also new to matlab