The utility concept is in charge of mapping indices from normal Matrix coordinates into the TwoD coordinate system. Here is an example of such a mapping for a banded matrix.

          [ 1  2  3    ]
 Matrix = [    4  5  6 ]
          [       7  8 ]
 

The element whose value is 4 is at (1,1) in Matrix coordinates. The TwoD mapping of this matrix would look as follows.

        [ 1  2  3 ]
 TwoD = [ 4  5  6 ]
        [ 7  8 ]
 

In TwoD coordinates the 4 is at (1,0).

There are three models of the Indexer concept, and each one provides a different mapping. There is the rect_indexer, the banded_indexer, and the diagonal_indexer. Used in oned_part, inside its iterators Called from by matrix_implementation::operator()(i,j) Called from by matrix_implementation::operator()(i,j)

• rect_indexer
• banded_indexer
• diagonal_indexer