# How to properly check that a Neumann/Robin boundary condition is satisfied **URL:** \ **Category:** General Discussion\ **Created:** [September 13, 2023, 7:19pm UTC](https://community.freefem.org/t/how-to-properly-check-that-a-neumann-robin-boundary-condition-is-satisfied/2705 "2023-09-13T19:19:25Z")\ **Posts on this page:** 1\ **Showing post:** 2
**Author:** ![cmd](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/cmd/32/67_2.png) [@cmd](https://community.freefem.org/u/cmd)\ **Post date:** [September 13, 2023, 8:16pm UTC](https://community.freefem.org/t/how-to-properly-check-that-a-neumann-robin-boundary-condition-is-satisfied/2705/2 "2023-09-13T20:16:28Z")
I did not say it was numerical noise (implies stochasticity), I said it was numerical error (due to discretization). You can check this by comparing with an analytical solution when possible (start simple!), or, in more complex cases, by comparing results on more accurate discretizations to demonstrate convergence. > [@Zero-flux boundary condition](https://community.freefem.org/t/zero-flux-boundary-condition/2699/6): > > It is due to numerical error. Your Neumann BC can only ever be as accurate as your discrete approximation of the derivatives. You can use a finer mesh or higher order elements if this is a problem, but I don’t expect errors of the order of 1e-9 to be an issue… --- _[View the full topic](https://community.freefem.org/t/how-to-properly-check-that-a-neumann-robin-boundary-condition-is-satisfied/2705)._