"Daniel Vasilaky" wrote in message <firstname.lastname@example.org>... > "Bjorn Gustavsson" <email@example.com> wrote in message > %Instead of unstable, what I should have said is that the pinv() is a discontinuous function of the data.
It is missleading to say PINV is the problem, the cause is we are dealing with ill-posed system
A*x = y.
No one claims PINV is the best approach to solve ill-posed problem, it is actually a bad one. This is well known for decated (century?).
PINV has a strict mathematical definition.
The main usage if PINV is to provides x that minimizes the 2-norm |x| subjected to |A*x - y| = min_z | A*z - y |.
It does NOT provide a stable solution x with respect to perturbation of y and A. It can be applied on many things, not exclusively for linear ill-posed system.