From 16ecfe4097e05a13e4437ea75273639b1a3800ae Mon Sep 17 00:00:00 2001
From: Damien Elmes <git@ichi2.net>
Date: Tue, 15 Nov 2011 19:15:12 +0900
Subject: [PATCH] add forgetting index adj; thanks to adam mesha for the
 inspiration

---
 anki/groups.py | 2 +-
 anki/sched.py  | 8 +++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/anki/groups.py b/anki/groups.py
index 120ea67bb..519ab22ed 100644
--- a/anki/groups.py
+++ b/anki/groups.py
@@ -71,7 +71,7 @@ defaultConf = {
         'ease4': 1.3,
         'fuzz': 0.05,
         'minSpace': 1,
-        'fi': 0.1,
+        'fi': [0.1, 0.1],
     },
     'maxTaken': 60,
     'mod': 0,
diff --git a/anki/sched.py b/anki/sched.py
index 4ec6f031a..a70b49e3d 100644
--- a/anki/sched.py
+++ b/anki/sched.py
@@ -2,7 +2,7 @@
 # Copyright: Damien Elmes <anki@ichi2.net>
 # License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
-import time, datetime, simplejson, random, itertools
+import time, datetime, simplejson, random, itertools, math
 from operator import itemgetter
 from heapq import *
 #from anki.cards import Card
@@ -581,9 +581,15 @@ gid in %s and queue = 2 and due <= :lim %s limit %d""" % (
             interval = (card.ivl + delay/2) * fct
         elif ease == 4:
             interval = (card.ivl + delay) * fct * conf['rev']['ease4']
+        # apply forgetting index transform
+        interval = self._ivlForFI(conf, interval)
         # must be at least one day greater than previous interval; two if easy
         return max(card.ivl + (2 if ease==4 else 1), int(interval))
 
+    def _ivlForFI(self, conf, ivl):
+        new, old = conf['rev']['fi']
+        return ivl * math.log(1-new) / math.log(1-old)
+
     def _daysLate(self, card):
         "Number of days later than scheduled."
         return max(0, self.today - card.due)