function xdot = examp3tnk(t,x)
% 4 Sept 13 - bwb
%   used in HW 1, due 5 Sept 13
%
% 3 tank example, with step change at t = 0
% linear, deviation variable form
%
  if t<0
      u = 0;
  else
      u = 1; % step change at t = 0
  end
  xdot(1) = -x(1) + u;
  xdot(2) = x(1) - x(2);
  xdot(3) = x(2) - x(3);
% make a row vector into a column vector
  xdot = xdot';