SuperMemo 2 PHP Implementation

.gitignore

composer.lock
/vendor

composer.json

{
    "require": {
        "symfony/console": "~2.6"
    }
}

no_recursive.php

<?php

require 'vendor/autoload.php';

function calcInterval($time = 1, $factor = 2.5, $oldInterval=1)
{
    if ($time < 1) {
        throw new \Exception('The number of repetitions must be 1 or higher');
    }
    if ($time == 1) {
        $interval = 1;
    } elseif ($time == 2) {
        $interval = 6;
    } else {
        $interval = $oldInterval * $factor;
    }

    return ceil($interval);
}

function calcNewFactor($oldFactor = 2.5, $quality = 4)
{
    if ($quality > 5 || $quality < 0) {
        throw new \Exception('Quality must be between 0 and 5');
    }

    $newFactor = $oldFactor + (0.1 - (5 - $quality) * (0.08 + (5 - $quality) * 0.02));

    return max($newFactor, 1.3);
}

$output = new \Symfony\Component\Console\Output\BufferedOutput();
$table = new \Symfony\Component\Console\Helper\Table($output);
$table->setHeaders(['', '1', '2', '3', '4', '5', '6', '7', '8', '9', '10']);

for ($q = 1; $q < 6; $q++) {
    $oldInterval = 1;
    $oldFactor = 2.5;
    $row = [$q];
    for ($n = 1; $n < 11; $n++) {
        $oldFactor = calcNewFactor($oldFactor, $q);
        $oldInterval = calcInterval($n, $oldFactor, $oldInterval);
        $row[] = $oldInterval;
    }

    $table->addRow($row);
}

$table->render($output);
echo $output->fetch();

# +---+---+---+----+----+-----+-----+------+------+-------+-------+
# |   | 1 | 2 | 3  | 4  | 5   | 6   | 7    | 8    | 9     | 10    |
# +---+---+---+----+----+-----+-----+------+------+-------+-------+
# | 1 | 1 | 6 | 8  | 11 | 15  | 20  | 26   | 34   | 45    | 59    |
# | 2 | 1 | 6 | 10 | 13 | 17  | 23  | 30   | 39   | 51    | 67    |
# | 3 | 1 | 6 | 13 | 26 | 47  | 79  | 121  | 167  | 218   | 284   |
# | 4 | 1 | 6 | 15 | 38 | 95  | 238 | 595  | 1488 | 3720  | 9300  |
# | 5 | 1 | 6 | 17 | 50 | 151 | 469 | 1501 | 4954 | 16844 | 58955 |
# +---+---+---+----+----+-----+-----+------+------+-------+-------+

recursive.php

<?php

require 'vendor/autoload.php';

function calcInterval($time = 1, $factor = 2.5)
{
    if ($time < 1) {
        throw new \RangeException('The number of repetitions must be 1 or higher');
    }

    if ($time == 1) {
        $interval = 1;
    } elseif ($time == 2) {
        $interval = 6;
    } else {
        $interval = calcInterval($time - 1, $factor) * $factor;
    }

    return ceil($interval);
}

function calcNewFactor($oldFactor = 2.5, $quality = 4)
{
    if ($quality > 5 || $quality < 0) {
        throw new \Exception('Quality must be between 0 and 5');
    }

    $newFactor = $oldFactor + (0.1 - (5 - $quality) * (0.08 + (5 - $quality) * 0.02));

    return $newFactor > 1.3 ? ($newFactor < 2.5 ? $newFactor : 2.5) : 1.3;
}

$output = new \Symfony\Component\Console\Output\BufferedOutput();
$table = new \Symfony\Component\Console\Helper\Table($output);
$table->setHeaders(['', '1', '2', '3', '4', '5', '6', '7', '8', '9', '10']);

for ($q = 1; $q < 6; $q++) {
    $oldInterval = 1;
    $oldFactor = 2.5;
    $row = [$q];
    for ($n = 1; $n < 11; $n++) {
        $oldFactor = calcNewFactor($oldFactor, $q);
        $oldInterval = calcInterval($n, $oldFactor, $oldInterval);
        $row[] = $oldInterval;
    }

    $table->addRow($row);
}

$table->render($output);
echo $output->fetch();

# +---+---+---+----+----+----+-----+-----+------+------+------+
# |   | 1 | 2 | 3  | 4  | 5  | 6   | 7   | 8    | 9    | 10   |
# +---+---+---+----+----+----+-----+-----+------+------+------+
# | 1 | 1 | 6 | 8  | 11 | 15 | 20  | 26  | 34   | 45   | 59   |
# | 2 | 1 | 6 | 10 | 11 | 15 | 20  | 26  | 34   | 45   | 59   |
# | 3 | 1 | 6 | 13 | 24 | 36 | 49  | 58  | 49   | 45   | 59   |
# | 4 | 1 | 6 | 15 | 38 | 95 | 238 | 595 | 1488 | 3720 | 9300 |
# | 5 | 1 | 6 | 15 | 38 | 95 | 238 | 595 | 1488 | 3720 | 9300 |
# +---+---+---+----+----+----+-----+-----+------+------+------+