[ublas] how to iterate over the elements of a mapped_matrix ?

Subject: [ublas] how to iterate over the elements of a mapped_matrix ?
From: rrossi_at_[hidden]
Date: 2011-02-07 13:13:48

Dear list, 

 i created a mapped_matrix and now i need to iterate over
the non_zero elements of SOME rows. 

say i need all of the elements of row
123... how should i get them? 

thanks in advance 

Riccardo