Samsara\Fermat\Provider\SeriesProvider

Complexity

Total Complexity

13

Size/Duplication

Total Lines	151
Duplicated Lines	0 %

Test Coverage

Coverage

66.67%

Importance

Changes	1
Bugs	0	Features	0

2 Methods

Rating	Name	Duplication	Size	Complexity
B	maclaurinSeries()	0	77	10
A	genericTwoPartSeries()	0	30	3

<?php

namespace Samsara\Fermat\Provider;

use Samsara\Exceptions\UsageError\IntegrityConstraint;
use Samsara\Exceptions\UsageError\OptionalExit;
use Samsara\Fermat\Numbers;
use Samsara\Fermat\Types\Base\Interfaces\Numbers\DecimalInterface;
use Samsara\Fermat\Types\Base\Interfaces\Numbers\NumberInterface;
use Samsara\Fermat\Types\Base\Interfaces\Numbers\SimpleNumberInterface;
use Samsara\Fermat\Values\ImmutableDecimal;

class SeriesProvider
{

    /**
     * Creates a series that evaluates the following:
     *
     * SUM[$startTerm -> infinity](
     *  $numerator($n) × $input^$exponent($n)
     *  --------------------------------
     *          $denominator($n)
     * )
     *
     * Where $n is the current term number, starting at $startTerm, and increasing by 1 each loop; where $numerator,
     * $exponent, and $denominator are callables that take the term number (as an int) as their only input, and give the
     * value of that section at that term number; and where $input is the x value being considered for the series.
     *
     * The function continues adding terms until a term has MORE leading zeros than the $precision setting. (That is,
     * until it adds zero to the total when considering significant digits.)
     *
     * @param SimpleNumberInterface $input
     * @param callable              $numerator
     * @param callable              $exponent
     * @param callable              $denominator
     * @param int                   $startTermAt
     * @param int                   $precision
     * @param int                   $consecutiveDivergeLimit
     * @param int                   $totalDivergeLimit
     *
     * @return ImmutableDecimal
     * @throws IntegrityConstraint
     * @throws OptionalExit
     */
    public static function maclaurinSeries(
        SimpleNumberInterface $input, // x value in series
        callable $numerator, // a function determining what the sign (+/-) is at the nth term
        callable $exponent, // a function determining the exponent of x at the nth term
        callable $denominator, // a function determining the denominator at the nth term
        int $startTermAt = 0,
        int $precision = 10,
        int $consecutiveDivergeLimit = 5,
        int $totalDivergeLimit = 10)
    {

        $sum = Numbers::makeZero($precision);
        $value = Numbers::make(Numbers::IMMUTABLE, $input->getValue(), $precision);

        $continue = true;
        $termNumber = $startTermAt;

        $adjustmentOfZero = 0;
        $prevDiff = Numbers::makeZero($precision);
        $prevSum = $sum;
        $divergeCount = -1;
        $persistentDivergeCount = -1;
        $currentPrecision = 0;

        while ($continue) {
            $term = Numbers::makeOne($precision);

            try {
                $exTerm = $value->pow($exponent($termNumber));
                $term = $term->multiply($exTerm);
                $term = $term->divide($denominator($termNumber));
                $term = $term->multiply($numerator($termNumber));
            } catch (IntegrityConstraint $constraint) {
                return $sum->truncateToPrecision($currentPrecision+1);
            }

            /** @var ImmutableDecimal $term */
            if ($term->numberOfLeadingZeros() >= $precision && !$term->isWhole()) {
                $continue = false;
            }

            $currentPrecision = $term->numberOfLeadingZeros();

            if ($term->isEqual(0)) {
                $adjustmentOfZero++;
            } else {
                $adjustmentOfZero = 0;
            }

            if ($adjustmentOfZero > 5) {
                $continue = false;
            }

            $sum = $sum->add($term);
            $currDiff = $sum->subtract($prevSum)->abs();

            if ($prevDiff->isLessThan($currDiff)) {
                $divergeCount++;
                $persistentDivergeCount++;
            } else {
                $divergeCount = 0;
            }

            if ($divergeCount == $consecutiveDivergeLimit || $persistentDivergeCount == $totalDivergeLimit) {
                throw new OptionalExit(
                    'Series appear to be diverging. Current diverge count: '.$divergeCount.' | Persistent diverge count: '.$persistentDivergeCount,
                    'A call was made to SeriesProvider::maclaurinSeries() that seems to be diverging. Exiting the loop.'
                );
            }

            $prevDiff = $currDiff;
            $prevSum = $sum;

            $termNumber++;
        }

        return $sum->roundToPrecision($precision);

    }

    /**
     * @param callable $part1
     * @param callable $part2
     * @param callable $exponent
     * @param int $startTermAt
     * @param int $precision
     *
     * @return ImmutableDecimal
     */
    public static function genericTwoPartSeries(
        callable $part1,
        callable $part2,
        callable $exponent,
        int $startTermAt = 0,
        int $precision = 10): ImmutableDecimal
    {

        $x = Numbers::makeZero($precision+1);

        $continue = true;
        $termNumber = $startTermAt;

        while ($continue) {
            $term = Numbers::makeOne($precision+1);

            /** @var ImmutableDecimal $term */
            $term = $term->multiply($part2($termNumber))->pow($exponent($termNumber))
                ->multiply($part1($termNumber));

            if ($term->numberOfLeadingZeros()-1 >= $precision) {
                $continue = false;
            }

            $x = $x->add($term);

            $termNumber++;
        }

        return $x->roundToPrecision($precision+1);

    }
    
}