>> Anyone can explain a bit about permutation_matrix class in lu.hpp,
>> please. I assume that it stores value i at position i.

>the permutation class in lu.hpp is actually a "swap-list" as produced by
>the LU factorization with pivoting algorithm. By default it is
>initialized as the identity permutation. Please refer to the swap_rows
>functions in lu.hpp for an example how to use such a permutation.

OK, I was confused because all functions had a const permutation_matrix passed as parameter.
Didnīt check the template functions that can modify it.

>>Current version has an inconvenience:  I would need a resize() method to reuse (when possible)
>>the underlying memory of its vector base class.

Reusing the underlying memory is still a requirement for me. Any ideas on why isn't that possible?