udpate docs

Author: balos1

Docs/source/SUNDIALS_Tutorial.rst

@@ -23,15 +23,18 @@ user-supplied reaction and diffusion coefficients:
 The inputs file contains a template for MRI approaches, where the diffusion process
 can be treated as a "fast" partition relative to the reaction process.
 
-The advection-diffusion examples at
-``amrex-tutorials/ExampleCodes/SUNDIALS/AdvDiff-HyprePrecon`` and
-``amrex-tutorials/ExampleCodes/SUNDIALS/AdvDiff-MLMGPrecon`` demonstrate
-SUNDIALS with preconditioning for an implicit diffusion solve using HYPRE and
-AMReX MLMG, respectively. The MLMG example can also use MLMG's HYPRE bottom
-solver interface when AMReX is built with HYPRE support. Their inputs also
-show how to select the SUNDIALS SPGMR
-preconditioning side with ``integration.sundials.linear_solver_preconditioning``.
-Please see each respective inputs file or
+The third example code at ``amrex-tutorials/ExampleCodes/SUNDIALS/AdvDiff-MLMGPrecon``
+solves the advection-diffusion equation, where :math:`A` and :math:`D` are
+user-supplied advection and diffusion coefficients:
+
+.. math:: \frac{\partial\phi}{\partial t} = D \nabla^2\phi - A \nabla\phi.
+
+The inputs file contains a template for IMEX approaches, where diffusion is
+treated implicitly with a SUNDIALS preconditioner that uses AMReX MLMG. The
+example can also use MLMG's HYPRE bottom solver interface when AMReX is built
+with HYPRE support.
+
+Please see the inputs file or
 `AMReX User Guide:Time Integration`_ for more details.
 
 .. _`AMReX User Guide:Time Integration`: https://amrex-codes.github.io/amrex/docs_html/TimeIntegration_Chapter.html#

ExampleCodes/SUNDIALS/AdvDiff-MLMGPrecon/Exec/README_sundials

@@ -3,4 +3,9 @@ for SUNDIALS installation, build, and usage instructions.
 
 Make sure that SUNDIALS_HOME in the GNUmakefile points to the installation directory.
 This tutorial also requires AMReX to be built with MLMG linear solver support.
-Set USE_HYPRE=TRUE and mlmg.use_hypre=1 to use MLMG's HYPRE bottom solver interface.
+The default inputs use a SUNDIALS IMEX-RK method with GMRES and an AMReX MLMG
+preconditioner for the implicit diffusion solve.
+
+Set USE_HYPRE=TRUE when building and mlmg.use_hypre=1 in inputs_sundials to use
+MLMG's HYPRE bottom solver interface. The HYPRE interface and options namespace
+are controlled by mlmg.hypre_interface and mlmg.hypre_options_namespace.