Method operator!=

uno/linear_algebra/SparseVector.hpp:33–35

         }

         friend bool operator!=(const iterator& a, const iterator& b) {
            return &a.vector != &b.vector || a.index != b.index;
         }

         friend bool operator==(const iterator& a, const iterator& b) {
            return &a.vector == &b.vector && a.index == b.index;