A PHP implementation of the SM-2 algorithm

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1.0.1 2014-04-24 19:56 UTC


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A PHP implementation of the SM-2 algorithm.


This is a library created by me to try out popular tools such as Travis, Packagist and Composer, as well as setting up a library structure and enhancing my understanding of test driven development. While being a test project for me, the library is still completely usable and could be used by any database of questions and answers to implement spaced repetition in an application.


  • Calculate the interval in which to repeat an item after the n:th repetition based on an E-factor.
  • Calculate an E-factor for an item based on the old factor (or no factor) and a response quality.


Memorize is installed through Composer. Add the following to your composer.json file.

    "require": {
        "wiwofone/memorize": "1.*"

The algorithm

SM is a family of algorithms made popular by the SuperMemo software package. The Memorize library implements the complete SM-2 algorithm in PHP. The SM2 class handles calculating repetition intervals and E-factors. The Card class handles flash cards and how many times they have been virtually repeated. Finally, the Repeater class handles actual repetition of a CardQueue, deciding which cards to repeat first and if they have been repeated successfully or not.


Run PHPUnit with $ phpunit in the root directory.