Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input float ones int(x2 x3)
1 22  5
1 17  6
1 20  3
1 15  4
1 18  2
1 20  3
1 16 10
1 19 20
1 14  8
1 14  1
end
I would like to implement the following expression manually
Array

where xi is a vector.
Array

Kindly, show me every possible steps as I am trying to learn and see how the above expression ends up containing sums of squares and cross products of the regressors. If my dataex is not appropriate, please use whatever seems appropriate. Thanks in advance!