function g = himmelblau_gradient1(x)
  %
  % A version of the himmelblau_gradient() function which takes a
  % column 2-vector instead of two distinct arguments. See
  % himmelblau_gradient.m for more information.
  %
  if (length(x) == 2)
    g = himmelblau_gradient(x(1), x(2));
  else
    g = NA;
  end
end
