How do I continue this loop?

connectivity=zeros(hel+vel,2);

ielem=0;

for i=1:vd+1

      for j=1:hd
          ielem = ielem+1;
          node_left=(hd+1)*(i-1)+j;
          node_right=node_left+1;
          connectivity(ielem,1)=node_left;
          connectivity(ielem,2)=node_right;
      end
  end
  for i=hd+1
      for j =1:vd
          ielem=ielem +1;
          node_down=(vd+1)*(j-1)+i;
          node_up=node_down + (hd+1);
          connectivity(ielem,1)=node_down;
          connectivity(ielem,2)=node_up;
      end
  end

It is returning a matrix with the second half of the matrix only returning zeros. I can only see that there is a problem with he second loop but I am having trouble spotting it. Any help would be amazing.

Thanks.

[Geoff Hayes]

Jack - please include all relevant code. What are the values for hd and vd and how are they related to hel and vel? Which matrix has the second half of the matrix only returning zeros? Is it connectivity?