sm2 0.1.4

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Implementation of SM-2 in DART.

SM-2 is a simple spaced repetition algorithm. It calculates the number of days to wait before reviewing a piece of information based on how easily the the information was remembered today.

Links #

The algorithm requires four inputs #

The algorithm requires four inputs: quality, repetitions, previous ease factor, and previous interval. The last three inputs are taken from the output of a previous call to SM-2. (On the first call, default values are used.)

Quality #

An integer from 0-5 indicating how easily the information was remembered today. This could correspond to a button such as "Difficult" or "Very Easy."

The official algorithm description explains the meaning of each number:

5 - perfect response
4 - correct response after a hesitation
3 - correct response recalled with serious difficulty
2 - incorrect response; where the correct one seemed easy to recall
1 - incorrect response; the correct one remembered
0 - complete blackout.

Repetitions (integer) #

The number of times the information has been reviewed prior to this review. repetitions should equal zero for the first review.

SM-2 uses this value to define specific intervals for the first and second reviews. SM-2 will also reset this value to zero when quality is less than 3.

Previous ease factor (float) #

A floating point number (≥ 1.3) generated by the last iteration of the SM-2 algorithm. previous ease factor should equal 2.5 for the first review.

The ease factor is used to determine the number of days to wait before reviewing again. Each call to SM-2 adjusts this number up or down based on quality.

Previous interval (integer) #

Generated by the last iteration of the SM-2 algorithm. Indicates the number of days to wait between reviews.

This previous interval is used when calculating the new interval. previous interval should equal zero for the first review.

Outputs #

The algorithm returns three outputs: interval, repetitions, and ease factor. All three values should be saved and passed to the next call to SM-2 as inputs.

Interval (integer) #

An integer number indicating the number of days to wait before the next review.

Repetitions (integer) #

The number of times the the information has been reviewed as of this review.

This value is maintained between calls to the algorithm and used for calculating interval. The number increments after each successful review. SM-2 will reset repetitions to zero if quality is less than 3.

Ease factor #

A floating point number (≥ 1.3) which is adjusted up or down based on how easily the information was remembered.

This value is maintained between calls to the algorithm and is used for calculating interval.

Steps #

If quality is greater than or equal to 3, indicating a correct response:

  1. If repetitions is 0 (first review), set interval to 1 day.
  2. If repetitions is 1 (second review), set interval to 6 days.
  3. If repetitions is greater than 1 (subsequent reviews), set interval to previous interval * previous ease factor. (See note about recursion below.)
  4. Round interval up to the next whole number.
  5. Increment repetitions by 1.
  6. Set ease factor to previous ease factor + (0.1 - (5 - quality) * (0.08 + (5 - quality ) * 0.02)). (See formula description below.)

If quality is less than 3, indicating an incorrect response:

  1. Set repetitions to 0.
  2. Set interval to 1.
  3. Set ease factor to previous ease factor (no change).

If ease factor is less than 1.3:

  1. Set ease factor to 1.3.

Return interval, repetitions and ease factor.

Ease factor formula #

After the first two reviews, ease factor is adjusted using this formula:

previous ease factor + (0.1 - (5 - quality) * (0.08 + (5 - quality) * 0.02))

The magic numbers come from the official algorithm description.

This increases ease factor when quality is 5, makes no change when quality is 4, and decreases ease factor by varying amounts when quality is lower than 4. The lower quality is, the more ease factor is decreased.

0.1.4 #

  • fix load file

0.1.3 #

  • Added example

0.1.0 #

  • Initial Open Source release.

example/README.md

example #

import 'package:flutter/material.dart';
import 'package:sm2/sm.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: HomePage(),
    );
  }
}
class HomePage extends StatelessWidget {

  final sm = Sm();
  
  @override
  @override
  Widget build(BuildContext context) {
    SmResponse smResponse = sm.calc(
      quality: 0,
      repetitions: 0,
      previousInterval: 2.5,
      previousEaseFactor: 0
    );
    return Scaffold(
      appBar: AppBar(
        title: Text('Spaced Repetition'),
        centerTitle: true,
      ),
      body: Container(
        padding: const EdgeInsets.all(10.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: <Widget>[
            Text("Repetitions: ${smResponse.repetitions}"),
            Text("Interval: ${smResponse.interval}"),
            Text("Ease Factor: ${smResponse.easeFactor}")
          ],
        ),
      ),
    );
  }
}

Use this package as a library

1. Depend on it

Add this to your package's pubspec.yaml file:


dependencies:
  sm2: ^0.1.4

2. Install it

You can install packages from the command line:

with Flutter:


$ flutter pub get

Alternatively, your editor might support flutter pub get. Check the docs for your editor to learn more.

3. Import it

Now in your Dart code, you can use:


import 'package:sm2/sm2.dart';
  
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23
Health:
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99
Maintenance:
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100
Overall:
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61
Learn more about scoring.

We analyzed this package on Dec 7, 2019, and provided a score, details, and suggestions below. Analysis was completed with status completed using:

  • Dart: 2.6.1
  • pana: 0.12.21
  • Flutter: 1.9.1+hotfix.6

Platforms

Detected platforms: Flutter

References Flutter, and has no conflicting libraries.

Health issues and suggestions

Document public APIs. (-1 points)

10 out of 10 API elements have no dartdoc comment.Providing good documentation for libraries, classes, functions, and other API elements improves code readability and helps developers find and use your API.

Format lib/sm2.dart.

Run flutter format to format lib/sm2.dart.

Dependencies

Package Constraint Resolved Available
Direct dependencies
Dart SDK >=2.1.0 <3.0.0
flutter 0.0.0
Transitive dependencies
collection 1.14.11 1.14.12
meta 1.1.7 1.1.8
sky_engine 0.0.99
typed_data 1.1.6
vector_math 2.0.8
Dev dependencies
flutter_test