function onedlaplace

for n = [10,20,40,80,160,320],

  h = 1/n;
  e = ones(n-1,1);
  A = spdiags([-e 2*e -e], -1:1, n-1, n-1);
  x = h*(1:n-1)';
  f = rhs(x);
  uapp = h^2*(A\f);
  
  u = sol(x);
  max(abs(u-uapp))
  subplot(2,1,1);
  plot(x,uapp,'r-',x,u,'b-');
  title(sprintf('n = %i', n ));
  makelarge
  subplot(2,1,2);
  plot(x,u-uapp,'r-');
  title('Fehler');
  makelarge
  pause
end


function f = rhs(x)
f = -12*x.^2 + 6*x;

function u = sol(x)
u = x.^3.*(x-1);