Function builtin_dt 

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

Student’s t density function.

dt(x, df) = gamma((df+1)/2) / (sqrt(df*pi) * gamma(df/2)) * (1 + x^2/df)^(-(df+1)/2)

@param x quantile vector @param df degrees of freedom @return numeric vector of densities