Cholesky benchmark

[gypsephi]

For evaluation purpose a benchmark of the Cholesky decomposition is needed.
Implement a Cholesky Benchmark using the Flow Graph API.

The following points have to be done:

• Understand the Cholesky decomposition (https://de.wikipedia.org/wiki/Cholesky-Zerlegung)
• Take a look into the Cholesky Benchmark of intel TBB (https://github.com/01org/tbb/blob/tbb_2019/examples/graph/cholesky/cholesky.cpp). There are 4 different Versions implemented and 2 of them using Flow Graph. The join graph based implementation is the important one for us. Try to understand it!
• Answer the following questions:
  • What kind of Flow Graph Nodes are used and why?
  • Do we have suitable Node in ProThOS to express the program and which do we need to add?
  • Can we reach good predictability (unrollability) of the Flow Graph?
• Create an issue for each missing Node Types
• Implement Cholesky Benchmark