fenics team mailing list archive

[Johan Hake <hake.dev@xxxxxxxxx>]

Very nice!

So:

  f*dx

will be assembled over all cells also if the mesh contains domain
information for some or all cells?

Johan

On 01/30/2013 09:32 AM, Martin Sandve Alnæs wrote:
> Hi all,
> yesterday I pushed a change to trunk, which fixes a long standing
> confusing issue. Unfortunately, the only way to stop this issue from
> confusing new users is to change the interpretation of some
> forms. Hopefully few codes will break from this change, but I'll explain
> it here so you can judge for yourself.
> 
> Previously dx, ds and dS were aliases for dx(0), ds(0) and dS(0)
> respectively, and the assembler in dolfin interpreted a missing
> meshfunction for subdomains as if all cells were labeled with 0. So if
> you wrote a form
>   u*v*dx      [1a]
> or
>   u*v*dx(0)   [1b]
> and assembled it without specifying subdomains, you got the integral
> over the entire mesh in both cases.
> 
> However if you wrote
>   f*dx + g*dx(1)   [2]
> and assembled it with subdomains, then f would only be integrated over
> the subdomain labeled 0, just as if you wrote
>   f*dx(0) + g*dx(1)   [3]
> This has naturally caused some confusion and bugs.
> 
> With the development version of ufc,ufl,ffc,dolfin from today, you can
> explicitly write
>   f*dx() + g*dx(1)   [4]
> to integrate f over the entire domain and g over subdomain 1,
> independent of subdomain labeling.
> 
> The breaking change is that [2] is now equivalent to [4], not [3].
> 
> That is, f*dx is now interpreted as f*dx(), and not as f*dx(0). This
> means that if you have code that depends on *dx being assembled only
> over subdomain 0, that code will break. I do not believe this to be a
> big problem, as it would be more natural to write explicitly dx(0) in
> such a case. However, if you do have such code, I recommend changing *dx
> to *dx(0) to be explicit, even if you are using 1.0 or 1.1 today.
> 
> Martin
> 
> 
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