Merge branch 'GEARRT_small_fix' into 'master'

GEARRT tiny fix.

See merge request !1648

doc/RTD/source/RadiativeTransfer/GEAR_RT.rst

@@ -30,7 +30,7 @@ Compiling for GEAR RT
     you to select a hydro Riemann solver, e.g ``--with-riemann-solver=hllc``.
 
 -   The thermochemistry requires the `grackle <https://github.com/grackle-project/grackle>`_ 
-    library. Grackle is a chemistry and cooling library presented in 
+    library version 3.2. Grackle is a chemistry and cooling library presented in 
     `B. Smith et al. 2017 <https://ui.adsabs.harvard.edu/abs/2017MNRAS.466.2217S>`_.
     Please note that the current implementation is not (yet) as
     advanced as the :ref:`GEAR subgrid model grackle cooling <gear_grackle_cooling>`, 

src/rt/GEAR/rt_thermochemistry_utils.h

@@ -239,17 +239,17 @@ rt_tchem_set_particle_radiation_field_for_test(
   const double time_to_cgs = units_cgs_conversion_factor(us, UNIT_CONV_TIME);
   const double t_Myr = time * time_to_cgs / (3600. * 24. * 365. * 1e6);
 
-  double fixed_fluxes[RT_NGROUPS];
-  for (int g = 0; g < RT_NGROUPS; g++) fixed_fluxes[g] = 0.;
+  /* NOTE: this assumes that the test is set up with 3 photon groups. */
+  double fixed_fluxes[3];
+  for (int g = 0; g < 3; g++) fixed_fluxes[g] = 0.;
 
   if (t_Myr < 0.5) {
     /* Be vocal, just in case somebody forgets you exist. */
     if (p->id == 1) message("Setting fixed radiation field.");
     /* Set fixed radiation fields, in cgs*/
-    fixed_fluxes[0] = 0.;
-    fixed_fluxes[1] = 1.350e01;
-    fixed_fluxes[2] = 2.779e01;
-    fixed_fluxes[3] = 6.152e00;
+    fixed_fluxes[0] = 1.350e01;
+    fixed_fluxes[1] = 2.779e01;
+    fixed_fluxes[2] = 6.152e00;
   }
 
   const double flux_to_cgs =