simplifying the code

pyomo/contrib/iis/mis.py

@@ -21,18 +21,9 @@
 
 from pyomo.opt import WriterFactory
 
-try:
-    from idaes.core.solvers import get_solver
-
-    have_idaes = True
-except:
-    have_idaes = False
-
 logger = logging.getLogger("pyomo.contrib.iis")
 logger.setLevel(logging.INFO)
 
-_default_nl_writer = WriterFactory.get_class("nl")
-
 
 class _VariableBoundsAsConstraints(IsomorphicTransformation):
     """Replace all variables bounds and domain information with constraints.
@@ -69,7 +60,7 @@ def _apply_to(self, instance, **kwds):
 
 
 def compute_infeasibility_explanation(
-    model, solver=None, tee=False, tolerance=1e-8, logger=logger
+    model, solver, tee=False, tolerance=1e-8, logger=logger
 ):
     """
     This function attempts to determine why a given model is infeasible. It deploys
@@ -87,7 +78,7 @@ def compute_infeasibility_explanation(
     Args
     ----
         model: A pyomo block
-        solver (optional): A pyomo solver, a string, or None
+        solver: A pyomo solver object or a string for SolverFactory
         tee (optional):  Display intermediate solves conducted (False)
         tolerance (optional): The feasibility tolerance to use when declaring a
             constraint feasible (1e-08)
@@ -99,12 +90,7 @@ def compute_infeasibility_explanation(
     # hold the original harmless
     modified_model = model.clone()
 
-    if solver is None:
-        if have_idaes:
-            solver = get_solver()
-        else:
-            raise ValueError("solver needed unless IDAES is installed")
-    elif isinstance(solver, str):
+    if isinstance(solver, str):
         solver = pyo.SolverFactory(solver)
     else:
         # assume we have a solver
@@ -252,10 +238,6 @@ def _constraint_generator():
             )
 
     # Phase 2 -- deletion filter
-    # TODO: the model created here seems to mess with the nl_v2
-    #       writer sometimes. So we temporarily switch to nl_v1 writer.
-    WriterFactory.register("nl")(WriterFactory.get_class("nl_v1"))
-
     # remove slacks by fixing them to 0
     for v in slack_block.component_data_objects(pyo.Var):
         v.fix(0)
@@ -305,8 +287,6 @@ def _constraint_generator():
         msg += "Constraints / bounds in guards for stability:"
         msg = _get_results(guards, msg)
 
-    WriterFactory.register("nl")(_default_nl_writer)
-
     logger.info(msg)