returns, via the function name, the value of the scalar product
is a sparse complex vector stored in compressed form, and
is a complex vector in full storage form.
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