Write function for find connect component

Write function for find connect component for the RCM algorithm.
Some improves at rcm.

The rcm function have a bug from the order_by_degree().

The ppnf() wasn't write yet.
Trying to write the correct output.
PCx with RCM run witout problem for one problem.
Write PPNF.

In this commit the function ppnf was write.

It still have to be tested and bugs removed.
Correct some bugs in PPNF.