function [ dval ] = D(t,x,u)
% 
% Written by:
% -- 
% John L. Weatherwax                2005-06-15
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
% Checked: 2006-01-02
% 
%-----
  
if( x >= 0.0 & x < 0.5 ) 
  dval(1) = 5; 
else
  dval(1) = 1;
end