I am looking at the following notes. I understand the math but I do not understand why is adding $d$ the same as deleting the i-th observation and fitting the usual model with just $X$ as explanatory variables but with one observation less.
Question 1: Although I understand the math, I do not understand the rationale behind how it is deleting the i-th observation. Can someone kindly explain to me please ? Thanks.
Question 2: And what would the matrix $d$ be if I want to delete multiple observations ? Can someone show me an example matrix please ?