VMS Help RTL Routines, MTH$, BLAS1$VxASUM, Returns  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    OpenVMS usage:floating_point
    type:         F_floating, D_floating, or G_floating real
    access:       write only
    mechanism:    by value

    The function value, called sum, is the sum of the absolute values
    of the elements of the vector x. The data type of the function
    value is a real number; for the BLAS1$VSCASUM, BLAS1$VDZASUM,
    and BLAS1$VGWASUM routines, the data type of the function value
    is the real data type corresponding to the complex argument data
    type.