Hi Mohammad, If you are using the compressed binary output format, the solver will produce a directory with each of the each of the files containing the appropriate field and information from each processor. Nektar++ utilities like FieldConvert can handle directories like this as an input. This is done for efficiency in writing the outputs – output is then not dependent on either a sequential or serial write – which would be very costly on large jobs. You can convert them to the newer HDF5 format (if you have compiled with it) by using FieldConvert i.e. FieldConvert <mesh> <session> *.chk *_hdf5.chk:out:format=Hdf5. I’ve never tried but running the command serially without the output module i.e by just loading in the new fld and dumping – may do what you’re asking – however probably not necessary and very inefficient. HDF5 will be more efficient in terms of space than compressed binary as well as just being a singular file – which is preferrable on certain file systems. You might also consider writing to HDF5 directly by including the flag -i Hdf5 in your run command. Hope this helps! Kind Regards, James. From: nektar-users-bounces@imperial.ac.uk <nektar-users-bounces@imperial.ac.uk> On Behalf Of m.r.rouhanian@ut.ac.ir Sent: Monday, November 7, 2022 12:32 AM To: nektar-users <nektar-users@imperial.ac.uk> Subject: [Nektar-users] Assemble the output files when using mpirun This email from m.r.rouhanian@ut.ac.ir<mailto: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 use the mpirun command to run a solver, dependent on the number of cores, chk format files produce (e.g. *_P0.chk, *_P1.chk, *_P2.chk, ...). Is there any way to assemble all of these .chk files and reconstruct a single output file containing all domain information? Best Regards, Mohammad