Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/Engineering.php
public static function DELTA($a, $b = 0)
    {
        $a = Functions::flattenSingleValue($a);
        $b = Functions::flattenSingleValue($b);

        return (int) ($a == $b);
    }
public static function DELTA($a, $b = 0)
    {
        $a = Functions::flattenSingleValue($a);
        $b = Functions::flattenSingleValue($b);

        return (int) ($a == $b);
    }
DELTA.

Tests whether two values are equal. Returns 1 if number1 = number2; returns 0 otherwise.
Use this function to filter a set of values. For example, by summing several DELTA
functions you calculate the count of equal pairs. This function is also known as the
Kronecker Delta function.

Excel Function:
DELTA(a[,b])

@param float $a the first number
@param float $b The second number. If omitted, b is assumed to be zero.

@return int