Quoting phil marinier <[email protected]>: > > > Date: Tue, 17 Nov 2009 01:05:17 +0100 > > From: [email protected] > > To: [email protected]; [email protected] > > Subject: Re: [FEniCS-users] "Expecting integrand to be an Expr instance." > error > > > > > > phil marinier wrote: > > > **I need to define a neumann bc on one edgeof a 2d rectangular domain. > > > When I try to compile my .ufl file, I get this error message: > > > > > > > > > This is FFC, the FEniCS Form Compiler, version 0.6.2. > > > For further information, visit http://www.fenics.org/ffc/. > > > > > > Preprocessing form file: Laplace.ufl --> Laplace.py > > > > > > Expecting integrand to be an Expr instance. > > > > > > *** FFC: Expecting integrand to be an Expr instance. > > > *** FFC: To get more information about this error, rerun FFC with --debug > > > > > > > > > My .ufl file is as follows: > > > > > > > > > element = FiniteElement("Lagrange", triangle, 1) > > > > > > v = TestFunction(element) > > > u = TrialFunction(element) > > > f = Function(element) > > > g = Function(element) > > > > > > ds0 = Integral("exterior facet", 0) > > > > > > a = inner(grad(v), grad(u))*dx + v*g*ds0 > > > L = v*f*dx
There seems to be some syntax confusion here. An Integral consists of an Integrand (here v*g) and a Measure so if you define from ufl.integral import * ds0 = Measure(Measure.EXTERIOR_FACET, 0) a = inner(grad(v), grad(u))*dx L = v*f*dx + v*g*ds0 it works. In fact the default ds is equal to ds0 as defined above. Calling a Measure with an integer (e.g., ds8 = ds(8) )will return a new Measure defined on the same domain type but on a different subdomain. > > > > > > I explicity defined ds0 so that I can specify which subdomain to > > > define the BC on. I assumed that if I used the default "ds" it would > > > define the BC over the entire circumferance. > > > Any help would be appreciated. Thank you > > > > > > Phil > > > > > You can you the default "ds" only for the subdomain you want to impose > > the BC. Take a look to this demo: > > > > demo/pde/elastodynamics/cpp > > > > or this thread: > > > > http://www.fenics.org/pipermail/fenics-users/2009-October/000169.html > > > > murtazo > > > > > > > > > > Ok so I looked at that demo, very helpful thank you, I was going to try > to use Assemble, but instead I can just create my VariationalProblem > and pass in the MeshFunctions as arguments. And for ds(0), ds(1), etc, the > number in the bracket is the marker that you give the subdomain. I got my > .ufl file to compile by using ds(0) instead of defining a ds0, so that fixes > my problem. Thank you again. Yes, this is the best way of solving your problem. Kristian > In case you guys would like the information about the error message, I had > originally tried compiling the above form file with the boundary term in L > instead of in a, but I got the same error message, so I assumed I was doing > it wrong and tried putting it in "a" instead, since an example I saw had > something like that. I seems like I can't compile anything that uses > "Integral." I used the command "ffc -l dolfin Laplace.ufl" to compile. > > Thank you again > > Phil > > > > > > _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
