more GPU updates

Docs/source/gpu.rst

@@ -34,13 +34,17 @@ value in the GPU kernel, the GPU gets access to the pointer to the
 underlying data.
 
 
+Most AMReX functions will work on the data directly on the GPU (like
+``.setVal()``).
 
-Most AMReX functions will work on the data directly on the GPU (like ``.setVal()``).
-
-In rare instances where we might need to operate on the data on the host, we
-can force a copy to the host, do the work, and then copy back.
+In rare instances where we might need to operate on the data on the
+host, we can force a copy to the host, do the work, and then copy
+back.  For an example, see the reduction done in  ``Gravity.cpp``.
 
+.. note::
 
+   For a thorough discussion of how the AMReX GPU offloading works
+   see :ref:`amrex-ecp`.
 
 
 Runtime parameters

Docs/source/refs.bib

@@ -1134,3 +1134,22 @@ @ARTICLE{doubledet2024
 title = {Sensitivity of Simulations of Double-detonation Type Ia Supernovae to Integration Methodology},
 journal = {The Astrophysical Journal},
 }
+
+
+@ARTICLE{amrex-ecp,
+       author = {{Myers}, Andrew and {Zhang}, Weiqun and {Almgren}, Ann and {Antoun}, Thierry and {Bell}, John and {Huebl}, Axel and {Sinn}, Alexander},
+        title = "{AMReX and pyAMReX: Looking Beyond ECP}",
+      journal = {arXiv e-prints},
+     keywords = {Computer Science - Distributed, Parallel, and Cluster Computing},
+         year = 2024,
+        month = mar,
+          eid = {arXiv:2403.12179},
+        pages = {arXiv:2403.12179},
+          doi = {10.48550/arXiv.2403.12179},
+archivePrefix = {arXiv},
+       eprint = {2403.12179},
+ primaryClass = {cs.DC},
+       adsurl = {https://ui.adsabs.harvard.edu/abs/2024arXiv240312179M},
+      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
+}
+