Hi, I think it might be that you are not defining the boundary conditions to use with the C0projection in the xml files since this requires inverting a global mass matrix. You could try using the option “localtoglobal” map. FieldConvert -m C0Projection:localtoglobalmap mesh.xml **.fld **-C0Proj.fld. Best, Spencer Sent from my iPhone On 24 Feb 2025, at 09:54, Gao <feigao2024@126.com> wrote: This email from feigao2024@126.com 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. And I use commond FieldConvert -m C0Projection mesh.xml **.fld **-C0Proj.fld. The <EXPANSIONS> in mesh.xml is as same as that in initial-condition.xml. <EXPANSIONS> <E COMPOSITE="C[33]" NUMMODES="4" TYPE="MODIFIED" FIELDS="rho,rhou,rhov,E" /> </EXPANSIONS> Could someone give me some advice? At 2025-02-23 17:10:32, "Gao" <feigao2024@126.com> wrote: Hello, I have much discontinuous (across element interface) distribution of variable in the fluid field. Why this happened? Then I want to use C0Projection module to smooth the fluid field. My mesh is third order, but the error comes ou below, and the other module of FieldConvert works. Fatal : Level 0 assertion violation Variable index out of range. terminate called after throwing an instance of 'Nektar::ErrorUtil::NekError' what(): Level 0 assertion violation Variable index out of range. Could someone give me some advice? With best regards _______________________________________________ Nektar-users mailing list Nektar-users@imperial.ac.uk https://mailman.ic.ac.uk/mailman/listinfo/nektar-users