|Summary:||Generalize replicate(.) to block diagonal replication|
|Product:||Eigen||Reporter:||Angelos Mantzaflaris <Angelos.Mantzaflaris>|
|Component:||Core - expression templates||Assignee:||Nobody <eigen.nobody>|
|Severity:||Feature Request||CC:||chtz, gael.guennebaud, jacob.benoit.1|
|Version:||3.3 (current stable)|
Description Angelos Mantzaflaris 2016-11-30 10:22:31 UTC
The Matrix::replicate(int) is very useful for writing compact formulas. I am also using (through the plugin mechanism) a similar expression, called blockDiag(int): Eigen::Matrix A; Eigen::Matrix B = A.blockDiag(3); produces the matrix exrpression: [ A 0 0 ] [ 0 A 0 ] [ 0 0 A ] The implementation is very similar to the replicate. This can be used eg. in the context of elasticity finite element matrices, if A are derivatives of scalar basis functions and the block diagonal expression provides derivatives of (3D) displacement vector. Maybe a better name could be Matrix::diagonalReplicate(int). Posting it here just in case that it is of interest for other purposes as well.
Comment 1 Gael Guennebaud 2016-11-30 17:04:00 UTC
This feature would be more powerful with a true concept of block-diagonal for which diagonalReplicate would only be a special case. Otherwise the special structure is lost.
Comment 2 Angelos Mantzaflaris 2016-11-30 17:56:18 UTC
Sure, that would be nice, then something like std::vector<Eigen::Matrix<double> > mVec(3); Eigen::BlockDiagonal<double> M(mVec); or Eigen::BlockDiagonal<double> M; M.append(A); M.append(B); M.append(C); to get [ A 0 0 ] [ 0 B 0 ] [ 0 0 C ] so that Eigen::BlockDiagonal<double> M(A,3); yields diagonalReplicate.
Comment 3 Nobody 2019-12-04 16:33:04 UTC
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