function ggprime=pderhsnew(t,gg,opt,k,dx,A,n)

heat=(k/dx^2)*A*gg;
% this one is from class
G=reshape(gg,n,n);
e=ones(n,1);
S=spdiags([e 0*e -e],-1:1,n,n);
S(n,1)=-1; S(1,n)=1;
ADV=S*G;
adv=reshape(ADV,n^2,1);

% this one makes it move in both directions (x and y)
% (added later)
%f=ones(n^2,1);
%T=spdiags([f 0*f -f],-1:1,n^2,n^2);
%T(1,n^2)=1;
%T(n^2,1)=-1;
%adv=T*gg;

ggprime=heat+10*adv;