<div dir="ltr">On Mon, Feb 18, 2013 at 3:11 PM, Kelly, Bernard J. (GSFC-660.0)[UNIVERSITY OF MARYLAND BALTIMORE COUNTY] <span dir="ltr"><<a href="mailto:bernard.j.kelly@nasa.gov" target="_blank">bernard.j.kelly@nasa.gov</a>></span> wrote:<br>
<div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">[re-sent, with smaller attachment]<br>
<br>
Hi Roland, and thanks for your reply. I'm still a bit confused, I confess<br>
(see below) ...<br>
<div class="im"><br>
<br>
On 2/16/13 12:38 AM, "Roland Haas" <<a href="mailto:roland.haas@physics.gatech.edu">roland.haas@physics.gatech.edu</a>> wrote:<br>
<br>
>Hello Bernard,<br>
><br>
>> Hi. Can someone explain to me why ML_BSSN calls SelectBoundConds within<br>
>> MoL_PostStep? It seems like the kind of once-off routine that would<br>
>>happen<br>
>> near the start of a simulation, rather than something that has to be<br>
>> performed every single timestep.<br>
>In the "new" boundary/symmetry interface (ie using thorn Boundary and<br>
>Symbase) one has to Select the variables for boundaries each time before<br>
>ApplyBCs is scheduled. There is a routine in Boundaries that clears the<br>
>selection.<br>
<br>
</div>OK; but can you tell me *why* this is? Why should we ever have to<br>
re-specify what kind of boundary conditions we use during a simulation,<br>
any more than we re-specify the evolution equations? Perhaps I don't<br>
really understand what "select the variables" means here.<br></blockquote><div><br></div><div style>Boundary conditions can be applied at different points during a simulation, and one may want to apply different boundary conditions at different times.</div>
<div style><br></div><div style>The canonical example is the conformal factor: While calculating initial conditions (e.g. with an elliptic solver), one wants to apply Robin boundary conditions; during evolution, one wants a radiative boundary condition. Similar arguments would hold if one were to enforce constraints during evolution.</div>
<div style><br></div><div style>-erik</div></div><div><br></div>-- <br>Erik Schnetter <<a href="mailto:schnetter@cct.lsu.edu" target="_blank">schnetter@cct.lsu.edu</a>><br><a href="http://www.perimeterinstitute.ca/personal/eschnetter/" target="_blank">http://www.perimeterinstitute.ca/personal/eschnetter/</a>
</div></div>