code: function rf(df1, df2) {
        var rchisqRatio;
  
        rchisqRatio = function(d) { return chisq.rchisq(d)() / d; };
  
        if (df1 <= 0 || df2 <= 0) { return function() { return NaN; }; }
  
        return function() {
           return rchisqRatio(df1) / rchisqRatio(df2);
        };
     }
docs: Returns a random variate from the F distribution, computed as a ratio
  of chi square variates.
  
  Expects `df1` and `df2` to be positive.
  
  @fullName rf(df1, df2)()
  @memberof f