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[Anders Logg <logg@xxxxxxxxx>]

On Thu, Sep 03, 2009 at 06:05:36PM +0200, Kristian Oelgaard wrote:
> Quoting Anders Logg <logg@xxxxxxxxx>:
>
> > I just fixed a bug in UFL for lhs/rhs when applied to mixed problems
> > and noticed some strange results for the generated quadrature
> > code. Nothing serious, but a bit annoying.
> >
> > There are two different demos in UFL: Stokes.ufl and StokesEquation.ufl.
> > They should give the same results. The results are the same for tensor
> > representation, but differ for quadrature. The difference is in the
> > following code:
> >
> > 1. Code generated from Stokes.ufl
> >
> >   // Number of operations for primary indices = 90
> >   for (unsigned int j = 0; j < 15; j++)
> >   {
> >     // Number of operations to compute entry = 6
> >     A[j] += (FE0_C0[ip][j]*F0 + FE0_C1[ip][j]*F1)*W9[ip]*det;
> >   }
> >
> > 2. Code generated from StokesEquation.ufl
> >
> >   // Number of operations for primary indices = 120
> >   for (unsigned int j = 0; j < 15; j++)
> >   {
> >     // Number of operations to compute entry = 8
> >     A[j] += (FE0_C0[ip][j]*F0 + FE0_C1[ip][j]*F1)*-1*-1*W9[ip]*det;
> >   }
> >
> > So we get an extra (-1)*(-1) which I guess should be possible to remove?
>
> Not really, the tree-format of the integrand that the quadrature transformer
> receives contains:
>
> Product
> (
>  IntValue(-1, (), (),{})
>  Product
>  (
>   IntValue(-1, (), (),{})
>   Sum
>   (
> [snip]
>
> one '-1' from F and one '-1' when applying rhs(F).
> The quadrature transformer (without optimisation) is not aware of any values, it
> just translates UFL objects into strings (you can use the -O option and they
> will be removed).
> To fix this 'bug' we should let UFL handle float values when expanding indices
> and derivatives. Note that this would probably mean that:
>
> -1*x*-1*y --> x*y, OK
> 2*(x + y) --> 2*x + 2*y, maybe not so nice
>
> In short, it is possible to remove but I don't know if it is worth the effort,
> if you want the same code in both cases use the -O option.
>
> Kristian

ok! Not a big issue.

--
Anders

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