ffc team mailing list archive

[Andy Ray Terrel <aterrel@xxxxxxxxxxxx>]

So the code built for me quite quickly (using a macbook - 1GB ram, dual 
core intel processor).  I am using the development version of ffc, fiat, 
and dolfin; perhaps that would help.  Just so you know your problem 
diverged when I used a P4-P3 element and the Crouziex-Raviart element 
(see below), I'm guessing that you need to look at something other than 
just the element.


vector = VectorElement("Crouzeix-Raviart", "triangle", 1)
scalar = FiniteElement("Discontinuous Lagrange", "triangle", 0)
mixed = vector+scalar

-- Andy

Chong Luo wrote:
> Sorry, I forgot to attach my code in the previous email.
>
> Best,
> Chong Luo
> ----- Original Message ----
> From: Chong Luo <luo.chong@xxxxxxxxx>
> To: Andy Ray Terrel <aterrel@xxxxxxxxxxxx>
> Cc: ffc-dev@xxxxxxxxxx
> Sent: Tuesday, March 25, 2008 5:05:31 PM
> Subject: Re: [FFC-dev] stable finite element for incompressible 
> nonlinear elasticity?
>
> Thank you very much for all those suggestions.
>
> I've attached my code for solving neoHookean elasticity (the 2D 
> version, which is much faster than the 3D one, but still blows up).
>
> I took "u" to be the mixture of (displacement, pressure), because the 
> NonlinearPDE solver
> subroutine pde.solve(u, t, T, dt) seems not accepting two functions 
> simultaneously. So I mix the (displacement, pressure) to be one 
> function "u" so that I can use the subroutine pde.solve(u, t, T, dt) 
> to solve.
>
> I'm not quite sure about how the NonlinearPDE solver works (I copied 
> the code from the /demo/pde/nonlinear-poisson). It seems that it  does 
> the job beautifully simple, but I don't know where to specify the 
> initial value of (displacement, pressure).
>
>
> Best,
>
> Chong Luo
>
> ----- Original Message ----
> From: Andy Ray Terrel <aterrel@xxxxxxxxxxxx>
> To: Chong Luo <luo.chong@xxxxxxxxx>; Discussion of FFC development 
> <ffc-dev@xxxxxxxxxx>
> Sent: Tuesday, March 25, 2008 9:04:06 AM
> Subject: Re: [FFC-dev] stable finite element for incompressible 
> nonlinear elasticity?
>
>
> > On the other hand, the one with (P1-P1) does compile, but the 
> computation is
> > not stable. What a life ...
> >
> > Also, maybe my NeoHookean.form is too complicated, it takes a lot of 
> time (5-10
> > minutes) to compile the form file.
> > And the size of NeoHookean.h is 4.8M, so it also takes a lot of time 
> to compile
> > main.cpp. Is there any way to speed up the compiling?
> >
>
>
> You need to add stabilization terms for P1-P1 to be a stable stokes
> element this is why the bilinear form has the delta*dot(grad(q),
> grad(p)) term in it.  I can't really see what is going on in your form
> but it appears that you are setting your trial and test functions to be
> the entire mixed space, this seems incorrect behaviour but it really
> depends on the parts that were left out of the form posted to the list.
>
> Another step is to try a P1-P0 element, this won't be as large (or
> accurate) as the P2-P1 element but should be more stable than just P1-P1
> with no stabilization terms.  For a long list of stable stokes elements
> I recommend Brezzi-Fortin.
>
> When compiling with very large .h files generated from ffc, one speedup
> I have found is to turn off all compiler optimizations.  (in g++ do -O0)
>
>
> Andy
>
>
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--

====================
Andy Terrel
Computer Science Dept
University of Chicago
aterrel@xxxxxxxxxxxx
---------------------

One machine can do the work of fifty men. 
No machine can do the work of one extraordinary man.
                                    -Elbert Hubbard