PGSL Version 4.0
I added a new routine to PGSL 4. This performs directional search, that is,
a line search in the improving direction. For some problem instances, there
is a dramatic improvement, especially for small problems. But for more difficult
problems involving large number of variables, there is a decrease in the performance.
(This is the classic "No Free Lunch" theorem).
This is why I hesitated to release this version for so long. In the end, I decided
to release this because hard problems are rare in practice. Even when there are
hard problems, we need only approximate solutions in engineering. Also, I believe
that if the problem is really hard and you need the exact solution, you should not
use a general purpose solver like PGSL, you should use a problem-specific search
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