Re: sparse matrix class implementation
Daniel T. wrote:
template < typename T >
class SparseMatrix {
std::map< std::pair< size_t, size_t >, T > rep;
public:
T operator()( size_t x, size_t y ) const {
return rep[ std::make_pair( x, y ) ];
}
T& operator()( size_t x, size_t y ) {
return rep[ std::make_pair( x, y ) ];
}
};
Add operations to taste. For example you might want to add a
member-function that tells wether a particular node exists.
IIRC, operator[] on a std::map will allocate a new entry if one does
not already exist, no?
T operator()(size_t x, size_t y) const {
std::map<std::pair<size_t, size_t>, T>::const_iterator mapItr =
rep.find(std::make_pair<size_t, size_t>(x, y));
if (mapItr != rep.end()) return mapItr->second;
else return 0;
}
This is of course overkill if you can control calls to operator() such
that it will never be called on a nonexistent location. But, since I
believe [] reduces to a map lookup anyway, the performace overhead is
minimal. The advantage is that routines written for standard matrices
can work with the above with filling your map with a bunch of zeroes.
Ryan
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