function vh=interp(v2h)

% Linear interpolation for multigrid
% F. Waleffe 11/15/2000

N2h =length(v2h); 
Nh=2*(N2h-1)+1; vh=zeros(Nh,1);

for j=2:N2h,
  vh(2*j-2)=(v2h(j-1)+v2h(j))/2;
  vh(2*j-1)=v2h(j);
end

vh(1)=v2h(1); vh(Nh)=v2h(N2h); % Dirichlet BC

