******************* 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 trying to implement a new solver using Nektar++ to solve the neutron diffusion equation. This equation has similar form as the Helmholtz equation. One of the differences between my case and all pre-existing solvers is that my solver requires using spatial-dependent constants for each finite element mesh. With the help of Dr. Cantwell I refered to cardiac electrophysiology solver ( in solvers/CardiacEPSolver/EquationSystems/Monodomain.cpp). I copied the code snippet of varying coefficients from CardiacEPSolver into my solver and made changes accordingly. However, something went wrong and it seems that the varying coefficient function does not work properly. I must have some misunderstanding of the variables or omitted some important details. Could anyone please take a look at attached note and see what happens? Thanks, Tengfei Zhang