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;;; gnosis-algorithm.el --- Spaced Repetition Algorithm for Gnosis -*- lexical-binding: t; -*-
;; Copyright (C) 2023-2024 Thanos Apollo
;; Author: Thanos Apollo <[email protected]>
;; Keywords: extensions
;; URL: https://git.thanosapollo.org/gnosis
;; Version: 0.0.1
;; Package-Requires: ((emacs "27.2") (compat "29.1.4.2"))
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with this program. If not, see <https://www.gnu.org/licenses/>.
;;; Commentary:
;; Handles date calculation as well as ef & interval calculations.
;; Gnosis implements a highly customizable algorithm, inspired by SM-2.
;; Gnosis algorithm does not use user's subjective rating of a note to
;; determine the next review interval, but instead uses the user's
;; success or failure in recalling the answer of a note.
;; Each gnosis note has an ef (easiness factor), which is a list of 3
;; values. The last value is the total ef for a note, which will be
;; used to determine the next interval upon a successful answer recall,
;; the second value is the ef-decrease value, this value will be
;; subtracted from the the total ef upon failure to recall the answer of
;; a note, the first value is the ef increase, will be added to the
;; total ef upon a successful recall.
;; Each gnosis deck has a gnosis-algorithm-ef-threshold, it's an
;; integer value that refers to the consecutive success or failures to
;; recall an answer. Upon reaching the threshold, gnosis-algorithm-ef-decrease
;; or gnosis-algorithm-ef-increase will be applied to the ef-increase or
;; ef-decrease of note.
;;; Code:
(require 'cl-lib)
(require 'calendar)
(defcustom gnosis-algorithm-proto '(0 1 2)
"Gnosis proto interval for the first successful reviews.
Values for the first proto successful intervals. There is no
restriction for list length."
:group 'gnosis
:type '(list integer))
(defcustom gnosis-algorithm-gnosis-value '(0.35 0.30 1.3)
"Starting gnosis score.
First item : Increase value (gnosis-plus)
Second item: Decrease value (gnosis-minus)
Third item : Total gnosis (gnosis-synolon/totalis) -> Total gnosis score"
:group 'gnosis
:type '(list float))
(defcustom gnosis-algorithm-amnesia-value 0.5
"Gnosis forgetting factor.
Used to calcuate new interval for failed questions.
The closer this value is to 0, the closer it is to total amnesia for
each a recall. This value should be less than 1.0."
:group 'gnosis
:type 'float)
(defcustom gnosis-algorithm-epignosis-value 0.1
"Value to increase gnosis-plus upon anagnosis.
Epignosis means knowledge accuracy.."
:group 'gnosis
:type 'float)
(defcustom gnosis-algorithm-agnoia-value 0.2
"Value to increase gnosis-minus upon anagnosis.
Agnoia refers to the lack of knowledge."
:group 'gnosis
:type 'float)
(defcustom gnosis-algorithm-anagnosis-value 3
"Threshold value for anagnosis event.
Anagosis is the process recognition & understanding of a context/gnosis.
Anagnosis events update gnosis-plus & gnosis-minus values, depending
on the success or failure of recall."
:group 'gnosis
:type 'integer)
(defcustom gnosis-algorithm-lethe-value 2
"Threshold value for hitting a lethe event.
Lethe is the process of being unable to recall a memory/gnosis.
On lethe events the next interval is set to 0."
:group 'gnosis
:type 'integer)
(defun gnosis-algorithm-replace-at-index (index new-item list)
"Replace item at INDEX with NEW-ITEM in LIST."
(cl-loop for item in list
for i from 0
collect (if (= i index) new-item item)))
(defun gnosis-algorithm-round-items (list)
"Round all items in LIST to 2 decimal places."
(cl-loop for item in list
collect (/ (round (* item 100)) 100.0)))
(defun gnosis-algorithm-date (&optional offset)
"Return the current date in a list (year month day).
Optional integer OFFSET is a number of days from the current date."
(cl-assert (or (numberp offset) (null offset)) nil "Date offset must be an integer or nil")
(let* ((now (decode-time))
(now (list (decoded-time-month now)
(decoded-time-day now)
(decoded-time-year now))))
(let ((date (if (zerop (or offset 0))
now
(calendar-gregorian-from-absolute
(+ offset (calendar-absolute-from-gregorian now))))))
(list (nth 2 date) (nth 0 date) (nth 1 date)))))
(defun gnosis-algorithm-date-diff (date &optional date2)
"Find the difference between DATE2 and DATE.
If DATE2 is nil, current date will be used instead.
DATE format must be given as (year month day)."
(let* ((given-date (encode-time 0 0 0 (caddr date) (cadr date) (car date)))
(date2 (if date2 (encode-time 0 0 0 (caddr date2) (cadr date2) (car date2))
(current-time)))
(diff (- (time-to-days date2)
(time-to-days given-date))))
(if (>= diff 0) diff (error "`DATE2' must be higher than `DATE'"))))
(cl-defun gnosis-algorithm-next-gnosis (&key gnosis success epignosis agnoia anagnosis
c-successes c-failures)
"Return the neo GNOSIS value. (gnosis-plus gnosis-minus gnsois-synolon)
Calculate the new e-factor given existing GNOSIS and SUCCESS, either t or nil.
Next GNOSIS is calculated as follows:
Upon a successful review, increase gnosis-synolon value (nth 2 gnosis) by
gnosis-plus value (nth 0 gnosis).
Upon a failed review, decrease gnosis-synolon by gnosis-minus value
(nth 1 gnosis).
ANAGNOSIS is an event threshold, updating either the gnosis-plus or
gnosis-minus values.
When C-SUCCESSES (consecutive successes) reach ANAGNOSIS,
increase gnosis-plus by EPIGNOSIS.
When C-FAILURES reach ANAGOSNIS, increase gnosis-minus by AGNOIA."
(cl-assert (listp gnosis) nil "Assertion failed: gnosis must be a list of floats.")
(cl-assert (booleanp success) nil "Assertion failed: success must be a boolean value")
(cl-assert (and (floatp epignosis) (< epignosis 1)) nil "Assertion failed: epignosis must be a float < 1")
(cl-assert (and (floatp agnoia) (< agnoia 1)) nil "Assertion failed: agnoia must be a float < 1")
(cl-assert (integerp anagnosis) nil "Assertion failed: anagosis must be an integer.")
(let ((anagnosis-p (= (% (max 1 (if success c-successes c-failures)) anagnosis) 0))
(neo-gnosis
(if success
(gnosis-algorithm-replace-at-index 2 (+ (nth 2 gnosis) (nth 0 gnosis)) gnosis)
(gnosis-algorithm-replace-at-index 2 (max 1.3 (- (nth 2 gnosis) (nth 1 gnosis))) gnosis))))
;; TODO: Change amnesia & epignosis value upon reaching a lethe or anagnosis event.
(cond ((and success anagnosis-p)
(setf neo-gnosis (gnosis-algorithm-replace-at-index 0 (+ (nth 0 gnosis) epignosis) neo-gnosis)))
((and (not success) anagnosis-p
(setf neo-gnosis
(gnosis-algorithm-replace-at-index 1 (+ (nth 1 gnosis) agnoia) neo-gnosis)))))
(gnosis-algorithm-round-items neo-gnosis)))
(cl-defun gnosis-algorithm-next-interval (&key last-interval gnosis-synolon success successful-reviews
amnesia proto c-fails lethe)
"Calculate next interval.
LAST-INTERVAL: Number of days since last review
C-FAILS: Total consecutive failed reviews.
GNOSIS-SYNOLON: Current gnosis-synolon (gnosis totalis).
SUCCESS: non-nil when review was successful.
SUCCESSFUL-REVIEWS: Number of successful reviews.
AMNESIA: 'Forget value', used to calculate next interval upon failed
review.
PROTO: List of proto intervals, for successful reviews.
Until successfully completing proto reviews, for every failed attempt
the next interval will be set to 0.
LETHE: Upon having C-FAILS >= lethe, set next interval to 0."
(cl-assert (booleanp success) nil "Success value must be a boolean")
(cl-assert (integerp successful-reviews) nil "Successful-reviews must be an integer")
(cl-assert (and (floatp amnesia) (<= amnesia 1)) nil "Amnesia must be a float <=1")
(cl-assert (< amnesia 1) nil "Value of amnesia must be lower than 1")
(cl-assert (and (integerp lethe) (>= lethe 1)) nil "Value of lethe must be an integer >= 1")
;; This should only occur in testing env or when the user has made breaking changes.
(let* ((last-interval (if (<= last-interval 0) 1 last-interval)) ;; If last-interval is 0, use 1 instead.
(interval (cond ((and (< successful-reviews (length proto))
success)
(nth successful-reviews proto))
;; Lethe event, reset interval.
((and (>= c-fails lethe)
(not success))
0)
(t (let* ((success-interval (* gnosis-synolon last-interval))
(failure-interval (* amnesia last-interval)))
(if success success-interval
;; Make sure failure interval is never
;; higher than success and at least 0
(max (min success-interval failure-interval) 0)))))))
(gnosis-algorithm-date (round interval))))
(provide 'gnosis-algorithm)
;;; gnosis-algorithm.el ends here
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