Math::SparseVector(3pm) on Linux
The text 6d67a23cd1cd, as Debian 9 (Stretch), Debian 8 (Jessie), Debian 7 (Wheezy) shipped it.
Supports sparse vector operations such as setting a value in a vector, reading a value at a given index, obtaining all indices, addition and dot product of two sparse vectors, and vector normalization.