adding model file for fisher 2-period model

HARK/models/fisher.py

@@ -0,0 +1,30 @@
+"""
+A model file for a Fisher 2-period consumption problem.
+"""
+
+from HARK.distribution import Bernoulli
+from HARK.model import Control
+
+# This way of distributing parameters across the scope is clunky
+# Can be handled better if parsed from a YAML file, probably
+# But it would be better to have a more graceful Python version as well.
+CRRA = 2.0,
+
+model = {
+    'shocks' : {},
+    'parameters' : {
+        'DiscFac' : 0.96,
+        'CRRA' : CRRA,
+        'Rfree' : 1.03,
+        'y' : [1.0, 1.0],
+        'BoroCnstArt' : None,
+    },
+    'dynamics' : {
+        'm' : lambda Rfree, a, y : Rfree * a + y,
+        'c' : Control(['m']),
+        'a' : lambda m, c : m - c
+    },
+    'reward' : {
+        'u' : lambda c : c ** (1 - CRRA) / (1 - CRRA)
+    }
+}