Function builtin_expm1 

fn builtin_expm1(
    args: &[RValue],
    _: &[(String, RValue)],
) -> Result<RValue, RError>

Numerically stable exp(x) - 1.

More accurate than exp(x) - 1 for x near zero, where catastrophic cancellation would otherwise lose precision.

@param x numeric vector @return numeric vector of exp(x) - 1