% Element stiffness matrix - 2D Laplace
%
% | a+b -a -b |
% |  -a  a  0 |
% |  -b  0  b |
%
function val=disco_stiff(i,j,ii,jj,indicator,dsr,Vdsr,Ndsr,hstep)
a=0.5*disco_rule(i,j,indicator,dsr,Vdsr,Ndsr,hstep);
b=a;
if (ii==1 & jj==1)
   val=a+b;
end
if (ii==1 & jj==2)
   val=-a;
end
if (ii==1 & jj==3)
   val=-b;
end
if (ii==2 & jj==1)
   val=-a;
end
if (ii==2 & jj==2)
   val= a;
end
if (ii==2 & jj==3)
   val= 0;
end
if (ii==3 & jj==1)
   val=-b;
end
if (ii==3 & jj==2)
   val= 0;
end
if (ii==3 & jj==3)
   val= b;
end
