add a test and a little doc for the scenario lp writer extension

doc/src/extensions.rst

@@ -15,6 +15,13 @@ extension can be included in some applications, but not others.
 There are a number of extensions, particularly for PH, that are provided
 with ``mpi-sppy`` and they provide examples that can be used for the
 creation of more. Extensions can be found in ``mpisppy.extensions``.
+Note that some things (e.g. some xhatters) can be used as a cylinder
+or as an extension. A few other things (e.g., cross scenario cuts) need
+both an extension and a cylinder.
+
+Many extensions are supported in :ref:`generic_cylinders`. The rest of
+this help file describes extensions released with mpisppy along with
+some hints for including them in your own cylinders driver program.
 
 Multiple Extensions
 -------------------
@@ -266,3 +273,12 @@ If some variables have zero probability in all scenarios, then you will need to
 ``do_not_check_variable_probabilities`` to True in the options for ``spbase``. This will result in skipping the checks for
 all variable probabilities! So you might want to set this to False to verify that the probabilities sum to one
 only for the Vars you expect before setting it to True.
+
+Scenario_lpwriter
+-----------------
+
+This extension writes an lp file with the model and json file with (a) list(s) of
+scenario tree node names and nonanticaptive variables for each scenario before
+the iteration zero solve of PH or APH. Note that for two-stage problems, all
+json files will be the same. See ``mpisppy.generic_cylinders.py``
+for an example of use.

examples/generic_cylinders.bash

@@ -20,7 +20,7 @@ echo "^^^ unpickle the sizes bundles and write the lp and nonant files ^^^"
 cd sizes
 python ../../mpisppy/generic_cylinders.py --module-name sizes --num-scens 10 --default-rho 1 --solver-name ${SOLVER} --max-iterations 0 --scenario-lpfiles --unpickle-bundles-dir sizes_pickles --scenarios-per-bundle 5
 cd ..
-echo "xxx also write a test?"
+echo "xxxx Early exit. xxxx"
 exit
 
 echo "^^^ pickle the scenarios ^^^"

mpisppy/tests/test_ef_ph.py

@@ -15,6 +15,7 @@
 
 import os
 import glob
+import json
 import unittest
 import pandas as pd
 import pyomo.environ as pyo
@@ -379,6 +380,45 @@ def test_xhat_extension(self):
         xhatobj1 = round_pos_sig(ph.extobject._xhat_looper_obj_final, 1)
         self.assertEqual(xhatobj1, 200000)
 
+
+    @unittest.skipIf(not pyo.SolverFactory('glpk').available(),
+                     "glpk is not available")
+    def test_scenario_lpwriter_extension(self):
+        print("test scenarip_lpwriter")
+        from mpisppy.extensions.scenario_lpfiles import Scenario_lpfiles
+        options = self._copy_of_base_options()
+        options["iter0_solver_options"] = {"mipgap": 0.1}    
+        options["PHIterLimit"] = 0
+        options["solver_name"] = "glpk"
+        options["tee_rank0_solves"] = True
+
+        ph = mpisppy.opt.ph.PH(
+            options,
+            self.all3_scenario_names,
+            scenario_creator,
+            scenario_denouement,
+            scenario_creator_kwargs={"scenario_count": 3},
+            extensions=Scenario_lpfiles,
+        )
+        conv, basic_obj, tbound = ph.ph_main()
+        # The idea is to detect a change in Pyomo's writing of lp files
+        with open("Scenario1_nonants.json", "r") as jfile:
+            nonants_by_node = json.load(jfile)
+        vname = nonants_by_node["ROOT"][0]  # first name in the file
+        gotit = False
+        with open("Scenario1.lp", 'r') as lpfile:
+            for line in lpfile:
+                if vname in line:
+                    gotit = True
+                    break
+        assert gotit, f"The first nonant in Scenario1_nonants.json ({vname}) not found in Scenario1.lp"
+        print("   deleting Scenario*.p and Scenario*_nonants.json")        
+        for fn in glob.glob("Scenario*.lp"):
+            os.remove(fn)
+        for fn in glob.glob("Scenario*_nonants.json"):
+            os.remove(fn)
+
+
     @unittest.skipIf(not solver_available,
                      "no solver is available")
     def test_wtracker_extension(self):