[Libmesh-users] variable number of variables per element

 [Libmesh-users] variable number of variables per element From: Danny Lathouwers - TNW - 2012-07-20 14:26:40 ```Dear all, I am looking into the suitability of Libmesh for our problem. We essentially have 5D problems (3 space and 2 additional independent variables). The 2 additional variables are handled by h-adaption and I am interested in having Libmesh deal with the spatial part (possibly by hp-refinement). The implication of our h-refinement scheme for the non-space coordinates is that we have a varying number of unknowns per spatial element to deal with (may be highly variable from 8 to hundreds of unknowns). Can Libmesh handle this situation? Note that I am mostly interested in using the storage, mesh adaption and quadrature etc., not so much in the matrix solvers... Thanks. Danny Lathouwers Delft University of Technology ```

 [Libmesh-users] variable number of variables per element From: Danny Lathouwers - TNW - 2012-07-20 14:26:40 ```Dear all, I am looking into the suitability of Libmesh for our problem. We essentially have 5D problems (3 space and 2 additional independent variables). The 2 additional variables are handled by h-adaption and I am interested in having Libmesh deal with the spatial part (possibly by hp-refinement). The implication of our h-refinement scheme for the non-space coordinates is that we have a varying number of unknowns per spatial element to deal with (may be highly variable from 8 to hundreds of unknowns). Can Libmesh handle this situation? Note that I am mostly interested in using the storage, mesh adaption and quadrature etc., not so much in the matrix solvers... Thanks. Danny Lathouwers Delft University of Technology ```
 Re: [Libmesh-users] variable number of variables per element From: John Peterson - 2012-07-20 14:45:32 ```On Fri, Jul 20, 2012 at 8:26 AM, Danny Lathouwers - TNW wrote: > Dear all, > > I am looking into the suitability of Libmesh for our problem. We essentially have 5D problems (3 space and 2 additional independent variables). Can you be more specific about "additional independent variables"? I assume your application is neutron transport? > The 2 additional variables are handled by h-adaption and I am interested in having Libmesh deal with the spatial part (possibly by hp-refinement). The implication of our h-refinement scheme for the non-space coordinates is that we have a varying number of unknowns per spatial element to deal with (may be highly variable from 8 to hundreds of unknowns). > Can Libmesh handle this situation? Libmesh can do subdomain-restricted variables, but that may not be fine-grained enough for what you are attempting. -- John ```
 Re: [Libmesh-users] variable number of variables per element From: Roy Stogner - 2012-07-20 15:59:53 ```On Fri, 20 Jul 2012, John Peterson wrote: > On Fri, Jul 20, 2012 at 8:26 AM, Danny Lathouwers - TNW > wrote: > >> The 2 additional variables are handled by h-adaption and I am >> interested in having Libmesh deal with the spatial part (possibly >> by hp-refinement). The implication of our h-refinement scheme for >> the non-space coordinates is that we have a varying number of >> unknowns per spatial element to deal with (may be highly variable >> from 8 to hundreds of unknowns). Can Libmesh handle this >> situation? > > Libmesh can do subdomain-restricted variables, but that may not be > fine-grained enough for what you are attempting. The big limitations: The code would have to pre-declare every variable. E.g. if you wanted to be able to go from a tensor product against zero spherical basis functions up to a tensor product against a couple dozen bases, then you'd need to call "add_variable" two dozen times and you'd need something in your "additional variable h-adaptation" that would detect and bomb out whenever something tried to do a 25th refinement step. Worse: you don't just want to declare 2000 variables and be done with it, because IIRC we've got a few places in library code where there's a loop over elements nested inside a loop over all variables. The formulation would either need to be hierarchic (the variables in each refined subdomain would be the same as the variables in the previous subdomain plus independent extras) or would need to have redundant variables plus fancy transformations at every single interface between subdomains. I'd strongly recommend the former. We were originally planning to do something similar for light radiation, but tabled them when our QoI turned out to be relatively radiation-insensitive. So the underlying code ought to be set up in the right direction, but it's never been tested on this scale. --- Roy ```