Portfolio model with income deduction scheme.

Documentation/CHANGELOG.md

@@ -14,6 +14,10 @@ Release Data: TBD
 
 #### Major Changes
 
+* Adds new consumption-savings-portfolio model `RiskyContrib`, which represents an agent who can save in risky and risk-free assets but faces
+frictions to moving funds between them. To circumvent these frictions, he has access to an income-deduction scheme to accumulate risky assets.
+PR: [#832](https://github.com/econ-ark/HARK/pull/832). See [this forthcoming REMARK](https://github.com/Mv77/RiskyContrib) for the model's details.
+
 #### Minor Changes
 
 * Fix bug in DCEGM's primary kink finder due to numpy no longer accepting NaN in integer arrays [#990](https://github.com/econ-ark/HARK/pull/990).

HARK/ConsumptionSaving/ConsRiskyAssetModel.py

@@ -1,10 +1,13 @@
 """
-This file contains classes and functions for representing, solving, and simulating
-agents who must allocate their resources among consumption, saving in a risk-free
-asset (with a low return), and saving in a risky asset (with higher average return).
+This file contains a class that adds a risky asset with a log-normal return
+factor to IndShockConsumerType.
+This class is not a fully specified model and therefore has no solution or
+simulation methods. It is meant as a container of methods for dealing with
+risky assets that will be useful to models what will inherit from it.
 """
 import numpy as np
 from copy import deepcopy
+from HARK.utilities import NullFunc
 from HARK.ConsumptionSaving.ConsIndShockModel import (
     IndShockConsumerType,  # PortfolioConsumerType inherits from it
     init_idiosyncratic_shocks,  # Baseline dictionary to build on
@@ -41,6 +44,10 @@ def __init__(self, cycles=1, verbose=False, quiet=False, **kwds):
             self, cycles=cycles, verbose=verbose, quiet=quiet, **kwds
         )
 
+        # These method must be overwritten by classes that inherit from
+        # RiskyAssetConsumerType
+        self.solve_one_period = NullFunc()
+
     def pre_solve(self):
         self.update_solution_terminal()