VPNs are very effective because they increase the cost of that kind of datasurvillenace of you enough to make it not worth it.
Not really, because you left out a huge asterisk. They are only effective after you have implemented a bunch of other methods to deal with cookies, tracking scripts, finger printing etc.
A vpn on it's own doesn't do shit if you don't auto wipe your cookies after every session for example. Which vpn marketing conveniently forgets to tell you
They're used for manipulating vectors.
Just like how in
a×v
the a makes the vector v longer or shorter, in
M×v
M can change the vector, for example rotate it.
Just like vectors and other mathematical objects, matrices are purely theoretical concepts. There is no direct real-life meaning to them.
However, there are a bunch of real-world problems where matrices can be put to use to calculate something meaningful.
Ironically rain flooding is usually solved with slower drainage