Question on adding matrix rows and columns

[Tobias Neckel]

Hello,

I need to weight and add a certain number of rows and columns from one matrix 
(A) into another one (B) where I just know the corresponding row and column 
indices, but not the indices of the entries inside one row or one column.

For the rows, I managed to do so by calling MatGetRow() (and MatRestoreRow()) on 
A, getting the corresponding column indices and values to work with and add into 
B.

For the columns, however, I just found MatGetColumnIJ() and MatGetColumnVector() 
in the online manual.
The first seems to give access to columns and corresponding indices, but I am 
not sure if n corresponds to the total number of columns or just all non-zero 
columns.
The latter (besides the warning of possibly being slow) seems to return the 
complete vector of values, but no indices. Is my interpretation correct so far?

A bit weired workaround would be to transpose A each time a column needs to be 
accessed and use MatGetRow() etc. again and retranspose afterwards. Or copying 
the transpose of A into another matrix meaning twice the amount of data in the 
RAM which I would like to avoid.

What would you suggest to do?

Thanks and best regards
Tobias

-- 
Dipl.-Tech. Math. Tobias Neckel

Institut für Informatik V, TU München
Boltzmannstr. 3, 85748 Garching

Tel.:   089/289-18602
Email:  neckel at in.tum.de
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