|Re: [eigen] Permuted Matrix|
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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] Permuted Matrix
- From: Manoj Rajagopalan <rmanoj@xxxxxxxxx>
- Date: Mon, 19 Jul 2010 19:57:33 -0400
- Organization: EECS Dept., University of Michigan, Ann Arbor, MI, USA
If implementing in Eigen is not possible for any reason, can you, for your
application, use the existing Eigen machinery as follows ...
The class Transpositions represents row/column interchanges. You can create
one for row-interchanges and one for column and then apply them using the *
operator like normal matrix multiplication.
eg: Transpositions rowTransp, colTransp; // initialize them
MatrixXd A(N,N), B(N,N);
B = rowTransp * A * colTransp; // () if/as necessary
If you want to store the product expression as a temporary then you will need
to use typedefs to "cache" the fairly-involved type expressions (using
ei_transposition_matrix_product_retval<> etc.). See Transpositions.h
Also, I see a Transpose<Transpositions<...> > and
Transpose<PermutationMatrix<...> > in the doxygen documentation. They might
be useful to you in achieving your objective indirectly.
On Monday 19 July 2010 05:39:11 pm ESCANDE Adrien 222264 wrote:
> I'd like to implement a permuted matrix i.e. a matrix P base on another M,
> such as P(i,j) = M(r[i], c[j]) for some permutation vectors r and c. It is
> very similar to the subject of another thread (how to create a "virtual"
> array or matrix) whose conclusion was to look at the way Minor class is
> Based on this Minor example, it is indeed easy to implement a
> PermutedMatrix class for read-only purpose. It goes like this:
> template<typename MatrixType> class PermutedMatrix
> : public MatrixBase<PermutedMatrix<MatrixType> >
> overload of coeff and coeffRef
> One can then access to coefficients of the matrix, use block expression,
> triangular view,...
> Writing in such a matrix is however a problem: PermutedMatrix can't have
> the DirectAccessBit bit because the "layout of the array of coefficients"
> is not "exactly the natural one suggested by rows(), cols(), outerStride(),
> innerStride(), and the RowMajorBit" DirectAccessBit documentation). Thus
> PermutedMatrix only derives from DenseCoeffsBase<Derived, false> and not
> DenseCoeffsBase<Derived, true>. In particular, it does not inherit the good
> operator() (Index, Index), and the copyCoeffByOuterInner(Index, Index,
> const DenseBase<OtherDerived>&) methods, the latter being needed in the
> Adding these missing methods directly in PermutedMatrix solves part of the
> problem: one can do P(i,j) = some_value or P = some_matrix, but they are
> still missing in expression based on PermutedMatrix , thus one can not do
> P.block(i,j,r,c) = another_matrix, because the copyCoeffByOuterInner of
> DenseCoeffsBase<Expr<PermutedMatrix<MatrixType> > > (in my example, Expr is
> Block) is not correctly defined.
> Do I miss something on this problem ? Any direction I could take, or flag I
> don't know of ? I'm not very familiar with Eigen internals yet, so any
> pointers would be welcome.
> Thank you,
> Adrien Escande