integer::i,k,p
real*8::w_laplace(4,ncells),d2(4),d4(4),shock_v,epson2,epson4
real*8::u,v,c,pp,pk
w_laplace=0.
d=0.
do i=1,nedges
k=iedge(3,i)
p=iedge(4,i)
if(p>0) then
w_laplace(:,k)=w_laplace(:,k)+0.5*(w(:,p)-w(:,k))
w_laplace(:,p)=w_laplace(:,p)+0.5*(w(:,k)-w(:,p))
end if
end do