returns, via the function name, the value of the scalar product
is a sparse real vector, stored in compressed form and
is a real vector in full storage format.
Dodson D S, Grimes R G and Lewis J G (1991) Sparse extensions to the Fortran basic linear algebra subprograms ACM Trans. Math. Software 17 253–263
Background information to multithreading can be found in the Multithreading