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.
% 
%-----
  
dval = zeros(length(u)); 

% The coefficient of \frac{ \partial^2 u }{ \partial x^2 } (\nu): 
dval(1,1) = 100;
% The coefficient of \frac{ \partial^2 \phi }{ \partial x^2 } (\eta): 
dval(2,2) = 100;