message: Another bugfix.
diff: @@ -304,6 +304,8 @@ void tree_gpu<cpu_root>::_derivative(const gfloat4 *coords,const gfloat4* forces
  subtree_sizes[tid] : tid + root - subtree_sizes[0] + 1;
  if (tid == 0)
  relative_offset = 0;
  + if (tid < subtree_sizes[0])
  + ft = force_torques[tid];
  if (tid < num_nodes)
  c->values[c->flex_offset + relative_offset] = ft.second * axis;
  }
  