/sys$common/syshlp/helplib.hlb RTL Routines, MTH$, MTH$xATAN, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 tangent

    OpenVMS usage:floating_point
    type:         F_floating, D_floating, G_floating
    access:       read only
    mechanism:    by reference

    The tangent of the angle whose value (in radians) is to be
    returned. The tangent argument is the address of a floating-point
    number that is this tangent. For MTH$ATAN, tangent specifies an
    F-floating number. For MTH$DATAN, tangent specifies a D-floating
    number. For MTH$GATAN, tangent specifies a G-floating number.