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In order to improve maintainability and flexibility of the AMG I would like to see some code clean-up and modernization.

This issue should is a wish-list/feature request and a note to myself.

Here follows an incomplete list, which might grow while working on it...

• replace manual memory management with smart pointers
• the iterator of Hierarchy currently has some additional methods. These should be moved to the Element so that element can be stored in an other container.
• replace the manually implemented linked-list in Hierarchy by either std::deque or std::vector. The push_front feature isn't used anywhere.
• I don't see a reason for a deep copy in the AMG and the Hierarchy. We should try to keep this copy as shallow as possible. (see #64 (closed))
• The element-allocator of the Hierarchy is not used at all. This is at least surprising, as it is used as a rebound allocator.
• Why do we also clone the lhs, rhs, update vectors in the AMG copy-constrcor? The are recreated in pre(...) anyway.
• Remove construction traits.

And some strange features I'm unsure about...

• graph.hh:123 why should the internal type of the weight change, depending on the constness of the matrix?
• matrixhierarchy.hh:334 shouldn't origComm be const?

And some further wishes...

• factor out aggregation so far, that we pass in prolongation/restriction operators constructed somewhere else
• make restriction/prolongation fulfil the operator interface
• can we replace graph.hh with a modern graph implementation, perhaps maintained outside of Dune?
• twolevelsolver has a LevelContext while the AMG keep different hierarchies. Can we unify this?