consistent mechanism ids

[boeschf]

Mechanism ids are assigned by iterating through an unordered map within fvm_mechanism_data. This is sub-optimal as the ids depend on implementation defined behaviour. In particular, the ids are not consistent between libc++ and libstdc++. The ids, however, are part of the key used to produce unique random values for solving SDEs, and thus, we get different random values with different OSs/different standard libraries even when using the same global seed value. In order to achieve reproducible results, I propose to change the container in question to a ordered std::map.

[thorstenhater]

Yes, please. But, we are using a map of unsigned to mechanism which is built linearly. How about using a vector?
Then, we should have this layout:

std::vector<mechanism> mechanisms_;
std::vector<std::size_t> revpot_mechs_;
// more index maps for different kinds.

That should enable patterns like

• initialising all mechanisms
• compute current for a single kind
• etc

What do you think.

[boeschf]

that sounds interesting. I'll experiment and may extend the PR.