function tree = tree_getsubtree(treein,rix)
%   tree <- the subtree 結果得到的子樹
%   treein -> the source tree  輸入的初始樹
%   rix -> 在源二叉樹中子樹的索引值 subtree-index in source tree

tree = treein;
if rix>treein.maxsize,
    return; 
end
% 得到子樹
vin  = [rix];
vout = [1];
iix = 1;
while vin(iix)<=treein.maxsize,
  tree.nodetyp(vout(iix)) = treein.nodetyp(vin(iix));
  tree.node(vout(iix)) = treein.node(vin(iix));
  vin = [vin vin(iix)*2 vin(iix)*2+1];
  vout = [vout vout(iix)*2 vout(iix)*2+1];
  iix = iix+1;
end
return