Hi Mohammad, C0 projection is for continuous Galerkin expansion. If you have a ContField pointer exp and a physics field phys, the following projection operation can enforce the C0 continuity of phys, exp->FwdTrans(phys, coeffs); // coeffs = InvMassMatrix * phys exp->BwdTrans(coeffs, phys); // phys = MassMatrix * coeffs MultiplyByInvMassMatrix is only a wrapper for solving the global linear system and its function has been included in ContField::FwdTrans. MultiplyByInvMassMatrix is not used very often. Cheers Ankang ________________________________ From: nektar-users-bounces@imperial.ac.uk <nektar-users-bounces@imperial.ac.uk> on behalf of mohammadreza rouhanian <m.r.rouhanian@ut.ac.ir> Sent: 15 February 2022 09:19 To: nektar-users <nektar-users@imperial.ac.uk> Subject: [Nektar-users] C0 continuity problem This email from m.r.rouhanian@ut.ac.ir 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, When I solve the equation that has the gradient the C0 continuity doesn't satisfy. I want to know the function name that forces C0 continuity. Is it MultiplyByInvMassMatrix? Best Regards, Mohammad Reza