JS probability functions

probabilities.js

// probability that the event with the passed probability will NOT occur
function complement(p) {
	return 1 - p;
}

// probability that a and b will happen when neither outcome
// is affected by the other (accepts 1 or more arguments)
function intersectionOfIndependentEvents(a, b) {
	var ret = a;
	for (var i = 1; i < arguments.length; i++) {
		ret *= arguments[i];
	}
	return ret;
}

// probability that a or b will happen when neither outcome
// is affected by the other (accepts 1 or more arguments)
function unionOfIndependentEvents(a, b) {
	var ret = a;
	for (var i = 1; i < arguments.length; i++) {
		ret = ret + arguments[i] - ret * arguments[i];
	}
	return ret;
}

// returns probability of a sequence repeating any substring for
// repeatLength terms given that the sequence is seqLength terms long
// and is a random permutation with uniqueTermCount unique terms.
// See also: Find longest repeat: https://gist.github.com/Daniel-Hug/98ab6b17d77623e47329a5bf71229c17
function probabilityOfRepeatingThisLong(seqLength, repeatLength, uniqueTermCount) {
	var arr = [];
	var prob = 1 / Math.pow(uniqueTermCount, repeatLength);
	var maxBlockLength = seqLength - repeatLength;
	for (var i = 1; i < maxBlockLength; i++) {
		arr.push(prob);
	}
	// fix: repeating this long with different periods are not independent events
	return unionOfIndependentEvents.apply(null, arr);
}

intersection = probability that a and b will happen
Union = probability that a or b will happen