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[matrix] Diff of /pkg/TODO
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Diff of /pkg/TODO

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revision 1832, Tue May 1 10:18:27 2007 UTC revision 1833, Tue May 8 12:25:57 2007 UTC
# Line 121  Line 121 
121    
122  - make sure  M[FALSE, FALSE]  works for all Matrices  - make sure  M[FALSE, FALSE]  works for all Matrices
123    {e.g. fails for M <- Diagonal(4)}    {e.g. fails for M <- Diagonal(4)}
124    
125    - <sparse> %*% <dense>  {also in crossprod/tcrossprod}  currently always
126      returns <dense>, since --> Csparse_dense_prod --> cholmod_sdmult
127      and that does only return dense.
128      When the sparse matrix is very sparse, i.e. has many rows with only zero
129      entries, it would make much sense to return sparse.
130    
131    - sparse-symmetric + diagonal should stay sparse-symmetric
132      (only stays sparse): Matrix(0, 4, 4) + Diagonal(4, 1:4)
133    
134    - For a square sparse matrix 'b' {typically dgCMatrix or dgTMatrix},
135      we'd want a function  "Mat_plus_t_Mat" <- function(b) {....}
136      which computes the symmetric sparse matrix   b + t(b)
137      in way that never works with size-doubled vectors from  b@i etc..
138    
139    - ! <symmetricMatrix>  loses symmetry, both for dense and sparse matrices.
140      !M  where M is "sparseMatrix", currently always gives dense. This only
141      makes sense when M is ``really sparse''.

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