Gabriele No, I think prolongation="copy" would choose the spatial prolongation operator. InterpNumTimelevels = 1 might be the right choice. If you declare and allocate only a single time level, then the code will automatically fail if it tries to use older time levels.
-erik On Mon, Mar 8, 2021 at 10:32 AM Gabriele Bozzola <[email protected]> wrote: > > Hi Erik, > >> In this case, you can declare the grid function to use 0-th order time >> interpolation, and allocate only a single time level. This would do >> the same thing. I think the respective time prolongtation operator is >> called "copy". > > > Do I achieve this by setting the tags prolongation="copy" and > InterpNumTimelevels = 1 > in the declaration of the grid function in the interface.ccl? > > Thanks again, > Gabriele > > On Sun, Mar 7, 2021 at 10:05 AM Erik Schnetter <[email protected]> wrote: >> >> On Sat, Mar 6, 2021 at 1:58 PM Gabriele Bozzola >> <[email protected]> wrote: >> > >> > Hi Erik, >> > >> > thanks for your response: it is very useful. >> > >> > > > Also, is it a problem if I don't worry about the boundaries If I >> > > > want to interpolate the constraints onto a sphere? >> > > >> > > Yes it is. Interpolation requires a stencil, which requires boundaries. >> > >> > I suspected so. Then, going back to the question in the first email, you >> > said that I am essentially forced to compute the diagnostic at >> > each timestep. The diagnostic I want to compute is very expensive, >> > and it would slow down dramatically the evolution, so I really want to >> > compute it only when I am going to output it. What I had in mind was >> > to copy grid function to the previous timelevels by setting _p and _p_p. >> > If I copy the same values as the one at the current time, this would >> > essentially disable time interpolation. But, if I output only when all >> > the refinement levels at the same time, this should not be a problem, >> > because there shouldn't be a need for time prolongation, right? >> >> In this case, you can declare the grid function to use 0-th order time >> interpolation, and allocate only a single time level. This would do >> the same thing. I think the respective time prolongtation operator is >> called "copy". >> >> -erik >> >> > Thanks again for your help, >> > Gabriele >> > >> > On Sat, Mar 6, 2021 at 7:45 AM Erik Schnetter <[email protected]> >> > wrote: >> >> >> >> On Fri, Mar 5, 2021 at 8:01 PM Gabriele Bozzola >> >> <[email protected]> wrote: >> >> > >> >> > Hi Erik, >> >> > >> >> > thank you very much for your answer. >> >> > >> >> > Just a clarification: what is 'boundary' exactly in this context? >> >> >> >> "Boundary" in the context are all grid points where the constraints >> >> cannot be calculated directly, i.e. by evaluating finite differences. >> >> >> >> > Also, is it a problem if I don't worry about the boundaries If I >> >> > want to interpolate the constraints onto a sphere? >> >> >> >> Yes it is. Interpolation requires a stencil, which requires boundaries. >> >> >> >> Cactus interpolation supports taking derivatives during interpolation. >> >> You can thus interpolate the ADM variables and their derivatives onto >> >> a sphere, and calculate the constraints there. You won't need to take >> >> derivatives on the sphere since you interpolated all derivatives, so >> >> evaluating the constraints on points on a sphere is then a point-wise >> >> operation. The horizon finder does this (calculating the expansion, >> >> not the constraints, but both have equivalent requirements). >> >> >> >> -erik >> >> >> >> > Thanks, >> >> > Gabriele >> >> > >> >> > Erik Schnetter <[email protected]> writes: >> >> > >> >> > > Gabriele >> >> > > >> >> > > If you do not use the constraints, then you do not need to set >> >> > > the >> >> > > boundaries. That would simplify many things; for example, you >> >> > > can >> >> > > calculate them at any time, and you do not need to worry about >> >> > > time >> >> > > levels. However, you then need to be careful about visualization >> >> > > and >> >> > > reductions: You need to ensure that you don't accidentally >> >> > > visualize >> >> > > the boundaries, and you cannot perform vertex-centred reductions >> >> > > in >> >> > > Carpet because they need some boundary values. >> >> > > >> >> > > If you do need boundaries, then you need three time levels to >> >> > > allow >> >> > > prolongation on boundaries, and you are essentially forced to >> >> > > evaluate >> >> > > the constraints at every iteration. I recommend the schedule bin >> >> > > "MoL_PseudoEvolution" for this, which runs once per time step, >> >> > > after >> >> > > MoL's loop, at the right time (i.e. before restriction). >> >> > > >> >> > > -erik >> >> > > >> >> > > On Fri, Mar 5, 2021 at 11:01 AM Gabriele Bozzola >> >> > > <[email protected]> wrote: >> >> > >> >> >> > >> Hello, >> >> > >> >> >> > >> suppose (for clarity) that I want to write a thorn that >> >> > >> computes the constraint violations >> >> > >> as grid functions. Since this is a diagnostic, I don't need to >> >> > >> compute it at every iteration, >> >> > >> so I will add a parameter "compute every" and I will schedule >> >> > >> the computations in >> >> > >> CCTK_ANALYSIS. Then, I will be careful and make sure that >> >> > >> compute_every is a >> >> > >> multiple of when all the refinement levels are synced up. >> >> > >> >> >> > >> How are boundary conditions handled in this case? >> >> > >> >> >> > >> I can call Boundary_SelectGroupForBC every "compute_every" and >> >> > >> schedule the >> >> > >> corresponding functions in the scheduler. But, do I need to (1) >> >> > >> allocate multiple timelevels >> >> > >> for my grid functions, (2) do anything about filling previous >> >> > >> timelevels? >> >> > >> >> >> > >> I am looking at WeylScal4 as an example. The thorn has >> >> > >> parameters "compute_every", >> >> > >> the grid functions have 3 time levels, and >> >> > >> Boundary_SelectGroupForBC is called >> >> > >> every "compute_every", but nothing is done to fill the previous >> >> > >> timelevels. How does this >> >> > >> work? >> >> > >> >> >> > >> Assuming that the boundary conditions are 'flat', is there any >> >> > >> way to just work with one >> >> > >> timelevel? >> >> > >> >> >> > >> Thanks, >> >> > >> Gabriele >> >> > >> >> >> > >> >> >> > >> _______________________________________________ >> >> > >> Users mailing list >> >> > >> [email protected] >> >> > >> http://lists.einsteintoolkit.org/mailman/listinfo/users >> >> >> >> >> >> >> >> -- >> >> Erik Schnetter <[email protected]> >> >> http://www.perimeterinstitute.ca/personal/eschnetter/ >> >> >> >> -- >> Erik Schnetter <[email protected]> >> http://www.perimeterinstitute.ca/personal/eschnetter/ -- Erik Schnetter <[email protected]> http://www.perimeterinstitute.ca/personal/eschnetter/ _______________________________________________ Users mailing list [email protected] http://lists.einsteintoolkit.org/mailman/listinfo/users
