Argument values (@argvals):
        a b c d
Min.    1 1 1 1
1st Qu. 2 2 2 2
Median  3 3 3 3
Mean    3 3 3 3
3rd Qu. 4 4 4 4
Max.    5 5 5 5

Observed functions (@X):
         a  b  c  d
Min.     1  2  3  4
1st Qu.  5  6  7  8
Median   9 10 11 12
Mean     9 10 11 12
3rd Qu. 13 14 15 16
Max.    17 18 19 20

