function st = collatzst (n)
%COLLATZST Compute the stopping time of n.
%

argmsg = nargchk (1, 1, nargin);
if (~isempty (argmsg))
  disp (argmsg);
  return;
end

st = zeros (size (n));

isodd = logical (mod (n, 2));
isnotone = (n - 1) > 0;

idxnotone = find (isnotone);
idxodds = find (isnotone & isodd);
idxevens = find (isnotone & (~isodd));

while (any (isnotone))
  
  n(idxodds) = 3 * n(idxodds) + 1;
  n(idxevens) = n(idxevens) / 2;

  st(idxnotone) = st(idxnotone) + 1;

  isodd = logical (mod (n, 2));
  isnotone = (n - 1) > 0;
  
  idxnotone = find (isnotone);
  idxodds = find (isnotone & isodd);
  idxevens = find (isnotone & (~isodd));
  
end

return;