gmcompo.m

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function rlabel = gmcompo(mesh);
% gmcompo: find connected components of a mesh
% returns an array (zba) holding labels, one label per
% node.

% use an n*alpha(n) union-find algorithm.

gdim = double(mesh{1});
di = double(mesh{2});


[scrap,numnode] = size(mesh{4});
parent = zba((0:(numnode-1))');
lsize = zba(ones(numnode,1));
tmplist = zeros(numnode,1);

[scrap,numelt] = size(mesh{5});

for snum = 0 : numelt - 1
  for whichnode = 0 : gdim - 1
    v = zeros(2,1);
    v(1) = double(mesh{5}(whichnode + 1, snum));
    v(2) = double(mesh{5}(whichnode + 2, snum));
    label = zeros(2,1);
    %% look up labels of v(1) and v(2)
    %% use path compression.
    for whichend = 1 : 2
      j1 = v(whichend);
      p = double(parent(j1));
      tmplistsize = 1;
      tmplist(1) = j1;
      while p ~= j1
        tmplistsize = tmplistsize + 1;
        tmplist(tmplistsize) = p;
        j1 = p;
        p = double(parent(p));
      end
      for i = 1 : tmplistsize
        parent(tmplist(i)) = p;
      end
      label(whichend) = double(p);
    end
    if label(1) ~= label(2)
      % merge labels 1 and 2
      if lsize(label(1)) >= lsize(label(2))
        largerc = label(1);
        smallerc = label(2);
      else
        largerc = label(2);
        smallerc = label(1);
      end
      parent(smallerc) = largerc;
      lsize(largerc) = lsize(largerc) + lsize(smallerc);
      lsize(smallerc) = 0;
    end
  end
end

%% Now renumber the active labels.

renumlabel = cumsum(lsize > 0) - ones(numnode,1);
rlabel = zba(zeros(numnode,1));

for vnum = 0 : numnode - 1
  % Get the label of node vnum.  Apply path compression

  j1 = vnum;
  p = double(parent(j1));
  tmplistsize = 1;
  tmplist(1) = j1;
  while p ~= j1
     tmplistsize = tmplistsize + 1;
     tmplist(tmplistsize) = p;
     j1 = p;
     p = double(parent(p));
  end
  for i = 1 : tmplistsize
    parent(tmplist(i)) = p;
  end
  rlabel(vnum) = renumlabel(p);
end