function  [sys, x0] = sfunmem(t,x,u,flag)
%SFUNMEM A one integration-step memory block S-function.
%
% This M-file is designed to be used in a SIMULINK S-Function block.
% It performs a one integration-step delay and hold "memory" function.
% Thus, no matter how large or small the last time increment was in the
% integration process, this function will hold the input variable from
% the last integration step.
%
% Use this function with a clock as input to get the step-size 
% of the simulation.
%
%	Copyright (c) 1990-94 by The MathWorks, Inc.
% Ned Gulley 2-19-92

if abs(flag) == 2,
  % If flag == 2, then SIMULINK is looking for the next point in real time. 
  % current state x gets current input u
  sys = u;

elseif flag == 3,
  % If flag == 3, then SIMULINK wants to know what the next output is.
  % current output y gets current state x
  sys = x;
  
elseif flag  == 0,
  % This part takes care of all initialization; it is used only once.
  % The system has only one discrete state, output, and input.
  % Significantly, this system has no direct feedthrough
  disp('Warning: The memory block should be replaced with a newer version.')
  disp('         This can be found in the SIMULINK block library under Nonlinear.')
  x0 = 0;
  sys = [0 1 1 1 0 0]';

else 
  % Flags not considered here are treated as unimportant.
  % Output is set to [].
  sys = [];

end