What is the best way to create a sparse array in C++?

Question

I am working on a project that requires the manipulation of enormous matrices, specifically pyramidal summation for a copula calculation.

In short, I need to keep

Answer 1

Small detail in the index comparison. You need to do a lexicographical compare, otherwise:

a= (1, 2, 1); b= (2, 1, 2);
(a

Edit: So the comparison should probably be:

return lhs.x