# SCM Repository

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

# Diff of /pkg/TODO

revision 1799, Sat Mar 24 14:54:00 2007 UTC revision 2005, Wed Jul 18 14:46:20 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      --> R/diagMatrix.R ('FIXME')
134      but also R/Ops.R  to ensure  sp-sym. + sp-sym. |-> sp-sym.  etc
135
136    - For a square sparse matrix 'b' {typically dgCMatrix or dgTMatrix},
137      we'd want a function  "Mat_plus_t_Mat" <- function(b) {....}
138      which computes the symmetric sparse matrix   b + t(b)
139      in way that never works with size-doubled vectors from  b@i etc..
140
141    - ! <symmetricMatrix>  loses symmetry, both for dense and sparse matrices.
142      !M  where M is "sparseMatrix", currently always gives dense. This only
143      makes sense when M is ``really sparse''.
144
145    - log1p(<sparseMatrix>) "should" give <dsparseMatrix>
146      Pretty surely, this would happen automagically, if "log1p" became part of
147      "Math" group generic ---> which is the case from R 2.6.0 on
148
149    - msy <- as(matrix(c(2:1,1:2),2), "dsyMatrix"); str(msy)
150
151      shows that the Cholesky factorization is computed ``too quickly''.
152      Can be a big pain for largish matrices, when it is unneeded.
153
154    - diag(m) <- val    currently automatically works via  m[cbind(i,i)] <- val
155      However,
156      we need methods for 'diag<-' at least for diagonalMatrix,
157      triangularMatrix, and probably also "dense*general*Matrix" since the
158      above currently goes via "matrix" and back instead of using the 'x' slot
159      directly.

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