In there is a discussion of rank deficient least-squares problem that includes some sensitivity issues, which are more complex than those for full-rank problems. It is stated that small changes in ...

In

there is a discussion of rank deficient least-squares problem that includes some sensitivity issues, which are more complex than those for full-rank problems. It is stated that small changes in

and
can cause large changes to the solution,

_LS
†
The sensitivity is related to the behavior of the pseudoinverse. Using