add NEWS.md

Author: hexaeder

NEWS.md

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+# NetworkDynamics Release Notes
+
+## v0.9 Changelog
+### Main changes in this release
+NetworkDynamics v0.9 is a complete overhaul of the previous releases of NetworkDynamics.
+Users of the package should probably read the new documentation carefully.
+
+The most important changes are:
+
+- Explicit split in `f` and `g` function: There is no split into `ODE` and
+  `Static` components anymore, verything is unified in component functions with
+  internal function `f` and output function `g`.
+- Parameters handling: Parameters are allways stored in a flat array. The
+  Symbolic Indexing Interfaces helps to set and retrieve parameters.
+- Automatic aggregation: vertices no longer receive a list of all connected
+  edges. This lead to inhomogeneous call signatures and was a performance
+  bottleneck. Now, each `Network` has a `aggregation` function attached to it.
+  The backaned will perform a reduction over all connected edges to calculate
+  the input for a certain vertex. In practice, for typical flow networks you'll
+  allways receive the sum of all flows rather than the individual flows.
+- Symbolic Indexing: the order of the states in the state vector changed in
+  non-trivial ways. But the old `idx_containing` and `syms_containing` functions
+  have been replaced with a much more capable symbolic indexing framework.
+
+### Limitations
+- We dropped support for delay differential equations. If you've been using that
+  feature please reach out to us.
+- Due to the built aggregation, the vertices cannot explicitly handle the inputs
+  from edges differently anymore. If you've been relying on those features reach
+  out to us.