Add comment about Andersen themostat and constraints

Per Michael's request at https://gerrit.gromacs.org/#/c/4479/

Refs #1695

Change-Id: Ibdd0de0e05b6d6be3fba8ba1d29f904b75c4d3c4

diff --git a/src/gromacs/mdlib/update.cpp b/src/gromacs/mdlib/update.cpp
index 140c2e3d37668ee33382d461193eada8fbdad1a9..638c1a646596370e341d87ac98919aec075f2ac4 100644 (file)
--- a/src/gromacs/mdlib/update.cpp
+++ b/src/gromacs/mdlib/update.cpp
@@ -2118,6 +2118,12 @@ extern gmx_bool update_randomize_velocities(t_inputrec *ir, gmx_int64_t step, co
 
     if (ir->etc == etcANDERSEN && constr != NULL)
     {
+        /* Currently, Andersen thermostat does not support constrained
+           systems. Functionality exists in the andersen_tcoupl
+           function in GROMACS 4.5.7 to allow this combination. That
+           code could be ported to the current random-number
+           generation approach, but has not yet been done because of
+           lack of time and resources. */
         gmx_fatal(FARGS, "Normal Andersen is currently not supported with constraints, use massive Andersen instead");
     }