Georgios, this is discussed very briefly in step-56: If you use an iterative solver like GMRES, you can solve systems with a 1 dimensional nullspace without problems. So what we do is that we just ignore that the pressure is not uniquely defined. If you want to ensure that your pressure has mean zero, you can do so after the fact as it is done in step-56. I assume this is the same for 46 and 22. Alternatively, you could fix one pressure DoF to 0 (we do this in step-56 so that UMFPACK works for the problem).
Best, Timo On Fri, Aug 17, 2018 at 11:57 AM <georgios.sialou...@gmail.com> wrote: > > Dear all, > > In step 46 (and step 22 too if possible) for stokes, how to we ensure that > the pressure is uniquely defined (i.e. that it is in L^2_0)? > > Kind regards, > Georgios > > -- > The deal.II project is located at > https://urldefense.proofpoint.com/v2/url?u=http-3A__www.dealii.org_&d=DwIBaQ&c=Ngd-ta5yRYsqeUsEDgxhcqsYYY1Xs5ogLxWPA_2Wlc4&r=4k7iKXbjGC8LfYxVJJXiaYVu6FRWmEjX38S7JmlS9Vw&m=bcIbcHElg1BGpLoA0M-tnKwLnDNHIcibLzDgJkMhwaE&s=VUIbItbKS23blT7ZU4GysP2lqkxgXsCbl0RW9nE60aY&e= > For mailing list/forum options, see > https://urldefense.proofpoint.com/v2/url?u=https-3A__groups.google.com_d_forum_dealii-3Fhl-3Den&d=DwIBaQ&c=Ngd-ta5yRYsqeUsEDgxhcqsYYY1Xs5ogLxWPA_2Wlc4&r=4k7iKXbjGC8LfYxVJJXiaYVu6FRWmEjX38S7JmlS9Vw&m=bcIbcHElg1BGpLoA0M-tnKwLnDNHIcibLzDgJkMhwaE&s=m8j4Ssra1gjdzNXPFfhJdqlEfqOfWwZghy7xbZzNl4M&e= > --- > You received this message because you are subscribed to the Google Groups > "deal.II User Group" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to dealii+unsubscr...@googlegroups.com. > For more options, visit > https://urldefense.proofpoint.com/v2/url?u=https-3A__groups.google.com_d_optout&d=DwIBaQ&c=Ngd-ta5yRYsqeUsEDgxhcqsYYY1Xs5ogLxWPA_2Wlc4&r=4k7iKXbjGC8LfYxVJJXiaYVu6FRWmEjX38S7JmlS9Vw&m=bcIbcHElg1BGpLoA0M-tnKwLnDNHIcibLzDgJkMhwaE&s=7N-i5PNeYieD4LtOPMSjoPoA625VXXlDgVY33XVClks&e=. -- Timo Heister http://www.math.clemson.edu/~heister/ -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
