function dx=cable(x,t)
  n=length(x);
  u=[exp(-t/10);x];
  du=zeros(u);
  for k=2:n
    du(k)=n^2/10/%pi^2*(u(k+1)-2*u(k)+u(k-1))
  end  
  du(n+1)=n^2/5/%pi^2*(-u(n+1)+u(n))
  dx=du(2:n+1);
endfunction

