[Dune-devel] [Dune-Commit] [Commit] dune-common - 64df627: Implement read-only IdentityMatrix
Oliver Sander
sander at igpm.rwth-aachen.de
Tue Dec 3 12:11:37 CET 2013
Hi Christoph,
> there is of course no real need for such a class: you can always use a FieldMatrix to represent an identity matrix. But isn't it tedious to initialize a dense matrix? With the new
> IdentityMatrix/DenseMatrixAssigner functionality you can now write:
>
> FieldMatrix< double, 2, 2 > Id = IdentityMatrix< double, 2 >();
>
I am using
FieldMatrix< double, 2, 2 > Id = ScaledIdentityMatrix< double, 2 >(1);
for that. That works just as well.
> 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?
> On
> the developer meeting in Aachen we agreed that jacobians may be implemented as slim "const" dense matrices that only cast into a field matrix. The IdentityMatrix simply implements this interface.
Documenting that interface is certainly a good idea.
As
> long as you don't need access to the entries of an identity matrix (do you ever need that?) you should prefer IdentityMatrix over another dense matrix as it holds no data at all.
I don't really ever use identity matrices at all. In particular not in such quantities
that make saving the one 'double' of ScaledIdentityMatrix worthwhile :-)
Cheers,
Oliver
>
> Cheers,
> Christoph
>
>
> On 12/03/2013 11:32 AM, Oliver Sander wrote:
>> Hi Christoph,
>> out of curiosity: what do you need such a matrix for?
>> Cheers,
>> Oliver
>>
>>
>> Am 03.12.2013 11:26, schrieb Christoph Gersbacher:
>>> New commit, appeared at Tue Dec 3 11:26:03 2013 +0100
>>> as part of the following ref changes:
>>>
>>> branch refs/heads/master updated from 79e8fa8 -> d58db46
>>>
>>> Browsable version: http://cgit.dune-project.org/repositories/dune-common/commit/?id=64df62745d93fbe6c380a039eebb5a3ac8f0da0c
>>>
>>> ======================================================================
>>>
>>> commit 64df62745d93fbe6c380a039eebb5a3ac8f0da0c
>>> Author: Christoph Gersbacher <christoph.gersbacher at mathematik.uni-freiburg.de>
>>> Date: Wed Oct 9 11:34:01 2013 +0200
>>>
>>> Implement read-only IdentityMatrix
>>> This implementation of an IdentityMatrix does not hold any data. It
>>> implements a reduced version of the DenseMatrix interface including a
>>> standard C++ cast operator to a Dune::FieldMatrix. This code illustrates
>>> the new forward capabilities of DenseMatrixAssigner.
>>>
>>> dune/common/CMakeLists.txt | 1 +
>>> dune/common/Makefile.am | 1 +
>>> dune/common/identitymatrix.hh | 160 ++++++++++++++++++++++++++++++++++++++++++
>>> 3 files changed, 162 insertions(+)
>>> create mode 100644 dune/common/identitymatrix.hh
>>>
>>>
>>>
>>> diff --git a/dune/common/CMakeLists.txt b/dune/common/CMakeLists.txt
>>> index 0075584..91ebd9e 100644
>>> --- a/dune/common/CMakeLists.txt
>>> +++ b/dune/common/CMakeLists.txt
>>> @@ -58,6 +58,7 @@ install(FILES
>>> genericiterator.hh
>>> gmpfield.hh
>>> hash.hh
>>> + identitymatrix.hh
>>> indent.hh
>>> interfaces.hh
>>> ios_state.hh
>>> diff --git a/dune/common/Makefile.am b/dune/common/Makefile.am
>>> index 189757a..4212515 100644
>>> --- a/dune/common/Makefile.am
>>> +++ b/dune/common/Makefile.am
>>> @@ -54,6 +54,7 @@ commoninclude_HEADERS = \
>>> genericiterator.hh \
>>> gmpfield.hh \
>>> hash.hh \
>>> + identitymatrix.hh \
>>> indent.hh \
>>> interfaces.hh \
>>> ios_state.hh \
>>> diff --git a/dune/common/identitymatrix.hh b/dune/common/identitymatrix.hh
>>> new file mode 100644
>>> index 0000000..646e398
>>> --- /dev/null
>>> +++ b/dune/common/identitymatrix.hh
>>> @@ -0,0 +1,160 @@
>>> +#ifndef DUNE_COMMON_IDENTITYMATRIX_HH
>>> +#define DUNE_COMMON_IDENTITYMATRIX_HH
>>> +
>>> +#include <dune/common/fmatrix.hh>
>>> +#include <dune/common/ftraits.hh>
>>> +#include <dune/common/math.hh>
>>> +#include <dune/common/std/constexpr.hh>
>>> +
>>> +/**
>>> + * \file
>>> + * \ingroup DenseMatVec
>>> + * \brief Implementation of an identity matrix that does not store
>>> + * any data.
>>> + * \author Christoph Gersbacher
>>> + */
>>> +
>>> +namespace Dune
>>> +{
>>> +
>>> + // IdentityMatrix
>>> + // --------------
>>> +
>>> + /** \class IdentityMatrix
>>> + *
>>> + * \ingroup DenseMatVec
>>> + *
>>> + * \brief Read-only identity matrix.
>>> + *
>>> + * Implementation of an identity matrix that does not store any data.
>>> + *
>>> + * \tparam K field type
>>> + * \tparam N dimension
>>> + */
>>> + template< class K, int N >
>>> + struct IdentityMatrix
>>> + {
>>> + /** \brief field type */
>>> + typedef K field_type;
>>> + /** \brief size type */
>>> + typedef std::size_t size_type;
>>> +
>>> + /** \brief return number of rows */
>>> + DUNE_CONSTEXPR size_type rows () const { return N; }
>>> + /** \brief return number of columns */
>>> + DUNE_CONSTEXPR size_type cols () const { return N; }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::mv */
>>> + template< class X, class Y >
>>> + void mv ( const X &x, Y &y ) const
>>> + {
>>> + y = x;
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::mtv */
>>> + template< class X, class Y >
>>> + void mtv ( const X &x, Y &y ) const
>>> + {
>>> + y = x;
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::umv */
>>> + template< class X, class Y >
>>> + void umv ( const X &x, Y &y ) const
>>> + {
>>> + y += x;
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::umtv */
>>> + template< class X, class Y >
>>> + void umtv ( const X &x, Y &y ) const
>>> + {
>>> + y += x;
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::umhv */
>>> + template< class X, class Y >
>>> + void umhv ( const X &x, Y &y ) const
>>> + {
>>> + y += x;
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::mmv */
>>> + template< class X, class Y >
>>> + void mmv ( const X &x, Y &y ) const
>>> + {
>>> + y -= x;
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::mmtv */
>>> + template< class X, class Y >
>>> + void mmtv ( const X &x, Y &y ) const
>>> + {
>>> + y -= x;
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::mmhv */
>>> + template< class X, class Y >
>>> + void mmhv ( const X &x, Y &y ) const
>>> + {
>>> + y -= x;
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::usmv */
>>> + template< class X, class Y >
>>> + void usmv ( const field_type &alpha, const X &x, Y &y ) const
>>> + {
>>> + y.axpy( alpha, x );
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::usmtv */
>>> + template< class X, class Y >
>>> + void usmtv ( const field_type &alpha, const X &x, Y &y ) const
>>> + {
>>> + y.axpy( alpha, x );
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::usmhv */
>>> + template< class X, class Y >
>>> + void usmhv ( const field_type &alpha, const X &x, Y &y ) const
>>> + {
>>> + y.axpy( alpha, x );
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::frobenius_norm */
>>> + typename FieldTraits< field_type >::real_type frobenius_norm () const
>>> + {
>>> + return std::sqrt( frobenius_norm2() );
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::frobenius_norm2 */
>>> + typename FieldTraits< field_type >::real_type frobenius_norm2 () const
>>> + {
>>> + return FieldTraits< field_type >::real_type( N );
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::infinity_norm */
>>> + typename FieldTraits< field_type >::real_type infinity_norm () const
>>> + {
>>> + return FieldTraits< field_type >::real_type( 1 );
>>> + }
>>> +
>>> + /** \copydoc Dune::DenseMatrix::infinity_norm_real */
>>> + typename FieldTraits< field_type >::real_type infinity_norm_real () const
>>> + {
>>> + return FieldTraits< field_type >::real_type( 1 );
>>> + }
>>> +
>>> + /** \brief cast to FieldMatrix */
>>> + operator FieldMatrix< field_type, N, N > () const
>>> + {
>>> + FieldMatrix< field_type, N, N > fieldMatrix( 0 );
>>> + for( int i = 0; i < N; ++i )
>>> + fieldMatrix[ i ][ i ] = field_type( 1 );
>>> + return fieldMatrix;
>>> + }
>>> + };
>>> +
>>> +} // namespace Dune
>>> +
>>> +#endif // #ifndef DUNE_COMMON_IDENTITYMATRIX_HH
>>>
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>>> Dune-Commit at dune-project.org
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>>>
>>
>>
>>
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