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[Till B <question143963@xxxxxxxxxxxxxxxxxxxxx>]

Question #143963 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/143963

    Status: Answered => Open

Till B is still having a problem:
ok, then I need PetSc or Trilinos. As I said, I have the precompiled Windows
version of Fenics. Is it possible to include these libraries into an
existing Fenics-installation? How do I do that?

Till


2011/2/3 Anders Logg <question143963@xxxxxxxxxxxxxxxxxxxxx>

> Your question #143963 on DOLFIN changed:
> https://answers.launchpad.net/dolfin/+question/143963
>
>     Status: Open => Answered
>
> Anders Logg proposed the following answer:
> On Thu, Feb 03, 2011 at 05:18:39PM -0000, Till B wrote:
> > Question #143963 on DOLFIN changed:
> > https://answers.launchpad.net/dolfin/+question/143963
> >
> >     Status: Answered => Open
> >
> > Till B is still having a problem:
> > Hi
> >
> > Thank you two for your answers.
> >
> > Anders:
> > With the working mesh, it solves a 37076 by 37076 matrix (which, however,
> is
> > singular). If I refine the mesh with the built-in refine function, I get
> a
> > 279286 by 279286 matrix (and here I get the memory problems).
> > The mesh file itself (in xml format) is around 650 kb at the moment. I
> > already tried meshes with 30mb (and then reduced the mesh density until I
> > arrived at a working version). Do you mean that the mesh.xml file does
> not
> > need much hard disk storage? Or that processing the mesh information
> should
> > not cause much memory usage?
>
> 300000x300000 is quite a big problem for UMFPACK. No wonder you run
> out of memory.
>
> It's unlikely that the storage of the mesh file itself will ever be a
> problem (you have more hard disk space than RAM). If it gets big, you
> can always gzip it. DOLFIN can read .xml.gz files.
>
> I meant that the storage (RAM) used by DOLFIN itself for meshes,
> vectors etc is (or should be) quite small. Your problem is UMFPACK, or
> in other words, that you use a direct solver instead of an iterative
> solver.
>
> > Andre:
> > The iterative stokes example does not work, it aborts with the message
> > "DOLFIN has not been configured with Trilinos or PETSc. Exiting.". I
> should
> > probably note that I use the precompiled Windows version of Fenics.
>
> If you want to solve any real problems with FEniCS, you need either
> PETSc or Trilinos.
>
> --
> Anders
>
>
> > Thank you so far
> >
> > Till
> >
> >
> > 2011/2/3 Anders Logg <question143963@xxxxxxxxxxxxxxxxxxxxx>
> >
> > > Your question #143963 on DOLFIN changed:
> > > https://answers.launchpad.net/dolfin/+question/143963
> > >
> > > Anders Logg proposed the following answer:
> > > On Thu, Feb 03, 2011 at 04:37:00PM -0000, Till B wrote:
> > > > New question #143963 on DOLFIN:
> > > > https://answers.launchpad.net/dolfin/+question/143963
> > > >
> > > > Hi,
> > > >
> > > > I recently installed the Fenics package and now I try to solve some
> > > problems with it. I want to simulate the flow of air around an
> obstacle.
> > > Eventually I want to include the temperature and see how a hot obstacle
> > > cools down in a colder air flow. However I encounter several problems,
> > > already with my baby example which does not even include the
> temperature. I
> > > am new in the CFD business. To begin, I adapted a few examples for
> > > Navier-Stokes solvers that I found in the Dolfin examples or on
> > > launchpad.net/nsbench (I tried both steady state and transient flow
> > > examples). I use a 3d mesh.
> > > >
> > > > My main problem occurs with mesh size. Unless I use a rather coarse
> mesh,
> > > I run out of memory, sometimes with a std::bad_alloc error, sometimes
> with
> > > the message that UMFPACK has run out of memory. It works with a mesh
> that
> > > has 7828 cells, but for example not, if I refine this mesh with the
> refine
> > > function of Dolfin.
> > > > Is there anything I can do about this? I could get more RAM, but I do
> not
> > > think that this will ultimately solve my problem. In the end I want to
> use
> > > much larger meshes.
> > > >
> > > > With this coarse mesh I do not get realistic results. Now matter how
> I
> > > set my inflow velocity, the speed of the fluid in the bulk is very low.
> When
> > > I use a 2d version of my example with a finer mesh, I get results that
> make
> > > sense.
> > > >
> > > > Is there a way to circumvent the memory issue?
> > > >
> > > > Thank you!
> > >
> > > What is the size of the linear systems you are solving? If you use P2
> > > elements in 3D you may very quickly get very large systems.
> > >
> > > I suspect the problem with memory allocation is a result of using a
> > > direct solver. UMFPACK allocates quite a lot of memory which makes it
> > > unsuitable for large problems.
> > >
> > > Try an iterative method and you should see that the memory usage is
> > > kept under control. The mesh itself should only require a minimal
> > > amount of storage.
> > >
> > >
> > >
> > > If you still need help, you can reply to this email or go to the
> > > following page to enter your feedback:
> > > https://answers.launchpad.net/dolfin/+question/143963
> > >
> > > You received this question notification because you are a direct
> > > subscriber of the question.
> > >
> >
>
> --
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>
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