Hedge May 2010

hedge@tiker.net

6 participants
32 discussions

Re: [Hedge] Problem running Maxwell 2D example, and question about creating custom operators

by David Powell

Hi Andreas, >> I have finally found some time to come back to hedge and start looking >> at implementing variable epsilon and mu in the Maxwell operator. So >> far I have succeeded in creating a very rough modification to em.py to >> allow the basic functionality (attached along with an modified example >> to run it). However, I'm having a couple of issues: >> >> - I'm unable to get the absorbing boundary conditions to work >> correctly. As far as I can see they should not need to be >> reformulated when varying epsilon and mu, since the internal value is >> always used. The current code looks correct to me, but it causes a >> TypeError exception and I'm not sure how to remedy this. > > This results from silliness in hedge's language that I've fixed a while > ago. If possible, you should use 'operator(argument)' instead of > 'operator * argument' in newly-written operator code. Otherwise, hedge > has to make a guess about how to bind things like 'operator * arg1 / > arg2', and in your case, it made a wrong guess. I introduced the 'op * > arg' syntax to allow cutesy expressions like 'dot(nabla, arg)', but > aside from these cases, I've come to the conclusion that the > parenthesized form is much less ambiguous. I've attached a diff for your > em.py that fixes this, along with a removal of tuple.count(), which is a > Py2.6ism. Hedge is still meant to run fine on Python 2.4. > Thankyou for this, absorbing boundaries now work fine. >> - I haven't been able to test a model where epsilon and mu have >> different values throughout the structure. The >> VariableVelocityStrongWaveOperator just sets velocity based on the >> spatial coordinates. However using this approach it's hard to >> guarantee that the mesh will coincide with the epsilon and mu >> variation, and it would be much more convenient to use tags. I have >> created examples structures in gmsh where I have tagged different >> volumes, however it seems that the material coefficient functions only >> have the "x" and "el" arguments, and neither of these carries tag >> information. Is there a way to do this that I am missing? > > See Mesh.tag_to_elements["my_tag"]. The gmsh reader should be filling > this with the tags read from the gmsh file. > I found this function and managed to get it working by creating element lists(?) corresponding to each tagged region. However I found that testing each element for membership of this list ("if el in region1_list" etc) was extremely slow. I tried an alternative approach by modifying each element to add epsilon and mu information to it, then getting my TimeDependantGivenFunction to use this value. This worked fine until I tried an MPI example, where it seemed that this information did not survive the distribution of the mesh between MPI nodes. Of course I am doing my initial testing without MPI but I don't want to inadvertently break MPI/GPU compatibility. >> - Is there any mechanism for asymmetric treatment or tagging of >> boundaries? In particular, once I have variable material constants >> working, the next thing I would like to implement is total >> field/scattered field incident boundary conditions, which would >> require different boundary flux operators in the total field and >> scattered field regions. > > I'm not quite sure what you're getting at here--are you talking about an > interior boundary between a total-field and a scattered-field region? Yes, this is exactly what I mean. See "Jens Niegemann, Michael Konig, Kai Stannigel, Kurt Busch, 'Higher-order time-domain methods for the analysis of nano-photonic systems', Photonics and Nanostructures – Fundamentals and Applications 7 (2009) 2–11" for an example of this being implemented (though they refer to Taflove's FDTD book for all the gory details of the total field/scattered-field implementation). The features in their DG code correspond to what I would be looking to implement in HEDGE if possible. > I do respect that you don't want to share your code right now. But a) > there's no reason to feel bad about any of it--in particular, it's a > work in progress and not a mess in any way, and b) if we had this > discussion out in the open, others could potentially learn from it. Plus > you're missing out on potentially useful feedback from others. > > Therefore I'd like to encourage you to involve the list in stuff like > this--there's nothing to lose, really. They're nice people. :) I have noticed the recent exchange of emails with Rafael on the list, so as soon as I have something which actually works I will post it to the list. I do have a couple more issues: Firstly, in the "max_eigenvalue" function of the MaxwellOperator, it seems that "discr" is an optional argument. However to turn the epsilon and mu from TimeDependentGivenFunction into arrays which I can multiply and find the maximum, wouldn't I need to interpolate them over "discr"? Can I just rely on it being passed in? Actually I was wondering if getting the user to pass a TimeDependentGivenFunction is really the best way to go about this. >From the user's point of view it would seem easiest to pass in a dictionary of tag names and corresponding (epsilon, mu) values. Secondly, and this isn't really a show stopper, just a nuisance, it seems that the MPI version freezes randomly on the maxwell-2d example when I use 4 or more CPUS (but strangely not 2 or 3). It just seems to stop part way through the time stepping, and doesn't seem repeatable. I'm using Ubuntu x64 9.10, boost 1.40.0, openmpi 1.3.2. I would assume this is some kind of deadlock problem, though of course the problem could be in MPI libraries rather than with HEDGE. I just thought I'd ask if you are able to reproduce this problem, if not then I will try switching to different MPI libraries. regards David

10 years, 5 months

Regression Check Failed

by Andreas Kloeckner

Hi there, I'm sorry to report that the regression check failed. Details are attached. - Your guilty conscience

10 years, 5 months

Regression Check Failed

by Andreas Kloeckner

Hi there, I'm sorry to report that the regression check failed. Details are attached. - Your guilty conscience

10 years, 6 months

Re: [Hedge] a new error

by Andreas Kloeckner

On Wed, 26 May 2010 17:04:12 -0400, "Field, Scott" <scott_field(a)brown.edu> wrote: > Sorry I've been so bothersome today. I was trying to update HEDGE, and when > I try to build pylo I get > > /users/kloeckner/mach/x86_64/pool/lib/gcc/x86_64-unknown-linux-gnu/4.3.3/include-fixed/features.h:159:1: > warning: this is the location of the previous definition > src/wrapper/wrap_silo.cpp: In function > 'int<unnamed>::silo_typenum_to_numpy_typenum(int)': > src/wrapper/wrap_silo.cpp:479: error: 'DB_LONG_LONG' was not declared in > this scope > error: command 'gcc' failed with exit status 1 > ------------------------------------------------------------------------ > COMMAND develop ON /users/sfield/src/pylo FAILED! > ------------------------------------------------------------------------ Oops. I fixed this in mid-April in pylo rev fb7582aab1f7..., which I apparently forgot to push to the web. It's up there now. Andreas

10 years, 6 months