[Boost-users] uBLAS sparse_matrix "default" value

Apparently the wheels of the ublas mailing list move slowly, so I'm asking this question here. Is there any way to set the "default" value of a sparse_matrix? sparse_matrix seems to guarantee that you always get a value when you access an index, even if that index hasn't been explicitly set. For sparse_matrix<float>, for instance, you get 0. Is there any way to specify this value? That is, if I wanted to get back, say, -1 for unset entries, is there a way to do this? There's no direct mention of this that I can find, although there were some discussions of zero-constructors or somesuch that may have been dealing with this question. Thanks. Austin Bingham