class TMatrixTSparse<float>: public TMatrixTBase<float>

TMatrixTSparse

Template class of a general sparse matrix in the Harwell-Boeing
format

Besides the usual shape/size decsriptors of a matrix like fNrows,
fRowLwb,fNcols and fColLwb, we also store a row index, fRowIndex and
column index, fColIndex only for those elements unequal zero:

fRowIndex[0,..,fNrows]:    Stores for each row the index range of
the elements in the data and column array
fColIndex[0,..,fNelems-1]: Stores the column number for each data
element != 0

As an example how to access all sparse data elements:

for (Int_t irow = 0; irow < this->fNrows; irow++) {
const Int_t sIndex = fRowIndex[irow];
const Int_t eIndex = fRowIndex[irow+1];
for (Int_t index = sIndex; index < eIndex; index++) {
const Int_t icol = fColIndex[index];
const Element data = fElements[index];
printf("data(%d,%d) = %.4e\n",irow+this->fRowLwb,icol+
this->fColLwb,data);
}
}

When checking whether sparse matrices are compatible (like in an
assigment !), not only the shape parameters are compared but also
the sparse structure through fRowIndex and fColIndex .

Several methods exist to fill a sparse matrix with data entries.
Most are the same like for dense matrices but some care has to be
taken with regard to performance. In the constructor, always the
shape of the matrix has to be specified in some form . Data can be
entered through the following methods :
1. constructor
TMatrixTSparse(Int_t row_lwb,Int_t row_upb,Int_t col_lwb,
Int_t col_upb,Int_t nr_nonzeros,
Int_t *row, Int_t *col,Element *data);
It uses SetMatrixArray(..), see below
2. copy constructors
3. SetMatrixArray(Int_t nr,Int_t *irow,Int_t *icol,Element *data)
where it is expected that the irow,icol and data array contain
nr entries . Only the entries with non-zero data[i] value are
inserted !
4. TMatrixTSparse a(n,m); for(....) { a(i,j) = ....
This is a very flexible method but expensive :
- if no entry for slot (i,j) is found in the sparse index table
it will be entered, which involves some memory management !
- before invoking this method in a loop it is smart to first
set the index table through a call to SetSparseIndex(..)
5. SetSub(Int_t row_lwb,Int_t col_lwb,const TMatrixTBase &source)
the matrix to be inserted at position (row_lwb,col_lwb) can be
both dense or sparse .