[Dune-devel] [Dune-Commit] [Commit] dune-common - 64df627: Implement read-only IdentityMatrix

[Christoph_Gersbacher]

Hi Oliver,
> I am using
>
> FieldMatrix< double, 2, 2 > Id = ScaledIdentityMatrix< double, 2 >(1);
>
> for that.  That works just as well.
That is indeed true. The ScaledIdentityMatrix correctly implements the 
method istl_to_fmatrix(), something other users have struggled with. 
IdentityMatrix only provides the standard C++ cast operator, which is 
more convenient and which was part of our discussion concerning the 
"const dense matrix" interface. You are right, I did add IdentityMatrix 
for documenting this new behavior.
>> Then, IdentityMatrix may be used as the return type of the methods jacobianTransposed() and jacobianInverseTransposed(); for some grids, the LocalGeometry's jacobians reduce to an identity matrix.
> When would that happen?  If LocalGeometry's jacobian is the identity that means that codim<0> entities are copies
> of their fathers.  And since the JacobianType is static _all_ entities would be copies of their fathers.
> What would I need such a grid for?
My bad, it is indeed somewhat more special. In PrismGrid, the upper and 
lower intersections of a grid element are images of the 
lower-dimensional host element after a translation. Lateral and 
horizontal intersections have individual geometry implementations, and I 
use dynamic polymorphism for choosing the correct local geometry 
implementation in the methods geometryInInside(), geometryInOutside(). 
Only for horizontal intersections the jacobians are the identity. I 
understand this is a very obscure example...

Cheers,
Christoph

-- 
Christoph Gersbacher<christoph.gersbacher at mathematik.uni-freiburg.de> 
<mailto:christoph.gersbacher at mathematik.uni-freiburg.de>
Abteilung für Angewandte Mathematik
Albert-Ludwigs-Universität Freiburg
Hermann-Herder-Str. 10
D-79104 Freiburg im Breisgau
Tel.: +49 (0)761 / 203 5645
Fax: +49 (0)761 / 203 5632
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