highlight distopia

- installation instructions
- link to docs for backends
- mini example
- mention (currently undocumented) MDAnalysis.lib.distances.HAS_DISTOPIA

Author: orbeckst

_posts/2025-03-11-release-2.9.0.md

@@ -50,7 +50,34 @@ For a full list of changes, bug fixes and deprecations see the [CHANGELOG][].
 
 * Support for Gromacs v2024.4 and v2025 TPR files.
 * A new "water" keyword for selecting water residues.
-* Support for [distopia][] 0.4.0 as an optional distance library backend.
+* Support for **[distopia][] 0.4.0** as an optional distance library
+  backend that now supports [many more distance
+  functions](https://docs.mdanalysis.org/stable/documentation_pages/lib/distances.html#id2)
+  for *all box types* (including general triclinic unit cells).
+  
+  On supported [x86-64][] platforms, install *distopia* with
+  ```bash
+  mamba install -c conda-forge distopia
+  ```
+  
+  You can then [enable *distopia* as a
+  backend](https://docs.mdanalysis.org/stable/documentation_pages/lib/distances.html#use-of-the-distopia-library)
+  to make use of the optimized *distopia* code for 
+  compute-intensive distance calculations, such as
+  [`distance_array()`](https://docs.mdanalysis.org/stable/documentation_pages/lib/distances.html#MDAnalysis.lib.distances.distance_array):
+  
+  ```python
+  protein = u.select_atoms("protein and not name H*")
+  lipids = u.select_atoms("resname POPC CHOL and not name H*")
+  d = MDAnalysis.lib.distances.distance_array(protein, lipids,
+                                              box=u.dimensions, 
+                                              backend="distopia")
+  ```
+  
+  If you want to see if *distopia* is available as a backend in a running
+  program, check that the variable `MDAnalysis.lib.distances.HAS_DISTOPIA` is
+  `True`.
+  
 * Parallel analysis support for `MDAnalysis.analysis.nucleicacids`, `MDAnalysis.analysis.contacts`, and `MDAnalysis.analysis.density`.
 * XYZ writer can now write positions up to a user-supplied precision via the `precision` keyword argument.