ufl team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Tue, Oct 21, 2008 at 06:03:27PM +0200, Martin Sandve Alnæs wrote:
> 2008/10/21 Anders Logg <logg@xxxxxxxxx>:
> > On Tue, Oct 21, 2008 at 05:41:15PM +0200, Martin Sandve Alnæs wrote:
> >> 2008/10/21 Anders Logg <logg@xxxxxxxxx>:
> >> > On Tue, Oct 21, 2008 at 05:27:55PM +0200, Anders Logg wrote:
> >> >> Is there a simple way to evaluate tensor expressions? For example, if
> >> >>
> >> >>  a = dot(v, u)*dx
> >> >>
> >> >> is there then a way to convert this to
> >> >>
> >> >>  v[0]*u[0] + v[1]*u[1] + ...
> >> >>
> >> >> ?
> >> >
> >> > I found the following in Dot:
> >> >
> >> >  def as_basic(self, dim, a, b):
> >> >      ii = Index()
> >> >      aa = a[ii] if (a.rank() == 1) else a[...,ii]
> >> >      bb = b[ii] if (b.rank() == 1) else b[ii,...]
> >> >      return aa*bb
> >> >
> >> > Why are the arguments dim, a and b required? A Dot already knows its
> >> > operands.
> >> >
> >> >> On Tue, Oct 21, 2008 at 05:27:55PM +0200, Anders Logg wrote:
> >> >> Is there a simple way to evaluate tensor expressions? For example, if
> >> >>
> >> >>  a = dot(v, u)*dx
> >> >>
> >> >> is there then a way to convert this to
> >> >>
> >> >>  v[0]*u[0] + v[1]*u[1] + ...
> >> >>
> >> >> ?
> >> >
> >> > I found the following in Dot:
> >> >
> >> >  def as_basic(self, dim, a, b):
> >> >      ii = Index()
> >> >      aa = a[ii] if (a.rank() == 1) else a[...,ii]
> >> >      bb = b[ii] if (b.rank() == 1) else b[ii,...]
> >> >      return aa*bb
> >> >
> >> > Why are the arguments dim, a and b required? A Dot already knows its
> >> > operands.
> >> >
> >>
> >> Because it is used in an algorithm that first expands its operands,
> >> so a and b here are not necessarily its original operands.
> >> As you see, dim is not used here, but it's used in some other Compounds.
> >>
> >> These functions could of course also be placed in the algorithm
> >> in question instead of in each Compound object, like with several
> >> other algorithms. But I think that's a detail we can discuss later,
> >> in context with other similar issues.
> >
> > Yes, if as_basic does not work like a member function, it seems
> > strange to make it a member function. Maybe it could be made static if
> > necessary.
> >
> 
> I'm fine with moving it into the algorithm, I can do that later.
> 
> Keeping it (static) in the class simplifies adding new Compound
> objects, that's the only reason I can think of now. But this is not
> really necessary since they would have to be handled in e.g. the
> latex compiler and maybe other places for that to make any sense.
> 
> This probably makes no sense to you right now, we should set
> up a session where I show how these things fit together.

There are a lot of things that don't make sense to me right now... :-)

So is there any way right now to handle compound expressions, or do I
need to implement it?

Say that I have a = dot(v, u)*dx, how can I expand it into simpler
operations (including only +, *, and [])?

-- 
Anders

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