******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* Dear all, I am using the robin boundary condition in Nektar+ but have some problems understanding how it works. The b.c. I want to impose is D* gradient {u} + 0.5 * u = 0 in which D is the diffusion constant (same as the D value used in the adjacent element), u is the unknown field. To do this I normalize the b.c. into the form of gradient {u} + 0.5 / D * u = 0, and specify the robin boundary condition as <R VAR="u" PRIMCOEFF="0.5/D" /> This setting does not yield the correct answer, unless the special case that D = 1.0. Could anyone please tell me what is wrong here? Thanks, Tengfei Zhang