Bugfix: Make MRI step fail when inner stepper has a recoverable error (…

…#456)

Fixes a bug where an MRI method would use the (likely corrupted) result
of an inner stepper which returned with a recoverable error. Once
adaptivity is supported, this could be handled similarly to ARK methods.

---------

Co-authored-by: David Gardner <gardner48@llnl.gov>

CHANGELOG.md

@@ -17,6 +17,9 @@ Fixed a bug in some Fortran examples where `c_null_ptr` was passed as an argumen
 to a function pointer instead of `c_null_funptr`. This caused compilation issues
 with the Cray Fortran compiler.
 
+Fixed a bug where `MRIStepEvolve` would not handle a recoverable error produced
+from evolving the inner stepper.
+
 Added CMake infrastructure that enables externally maintained addons/plugins
 to be *optionally* built with SUNDIALS. See the [Contributing Guide](./CONTRIBUTING.md)
 for more details.

doc/shared/RecentChanges.rst

@@ -19,3 +19,6 @@ instead of ``SameMajorVersion``. This fixes the issue seen
 Fixed a bug in some Fortran examples where ``c_null_ptr`` was passed as an argument
 to a function pointer instead of ``c_null_funptr``. This caused compilation issues
 with the Cray Fortran compiler.
+
+Fixed a bug where :c:func:`MRIStepEvolve` would not handle a recoverable error
+produced from evolving the inner stepper.

src/arkode/arkode_mristep.c

@@ -2139,7 +2139,7 @@ int mriStep_StageERKFast(ARKodeMem ark_mem, ARKodeMRIStepMem step_mem, int is)
   /* advance inner method in time */
   retval = mriStepInnerStepper_Evolve(step_mem->stepper, t0, ark_mem->tcur,
                                       ark_mem->ycur);
-  if (retval < 0) { return (ARK_INNERSTEP_FAIL); }
+  if (retval != 0) { return (ARK_INNERSTEP_FAIL); }
 
   /* post inner evolve function (if supplied) */
   if (step_mem->post_inner_evolve)