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/**
* Mathematical utilities.
* @module app/utils/math_utils
*/
/**
* RegExp to check if a string contains only hexadecimal values.
* The string should only contain the characters [0-9] or [a-f], case-insensitive.
* @type {RegExp}
*/
const HEXADECIMAL_REGEXP = new RegExp("^[a-f0-9]+$", "i");
/**
* Check if a string is a valid hexadecimal number.
* @param {String} text the string to check
* @return {Boolean} true if the string is a valid hexadecimal number
*/
export const isHexadecimal = (text) => !!text?.match(HEXADECIMAL_REGEXP);
/**
* Constrain a number between an upper or lower bound.
* @param {Number} value the value to clamp
* @param {Number} low the lower bound
* @param {Number} high the upper bound
* @return {Number} the clamped value
*/
export const clamp = (value, low = 0, high = 1) =>
value < low ? low : value < high ? value : high;
/**
* Implementation of mod that supports negative numbers (unlike JavaScript % operator)
* @param {Number} numerator the modulo numerator
* @param {Number} denominator the modulo denominator
* @return {Number} `numerator mod denominator`
*/
export const mod = (numerator, denominator) =>
numerator - denominator * Math.floor(numerator / denominator);
/**
* Get the mean of a list of numbers (where non-null)
* @param {Array} numbers list of numbers
* @return {number} arithmetic mean
*/
export const arrayMean = (numbers) => {
const nonZero = (numbers || []).filter((number) => !!number);
if (!nonZero.length) return 0;
const sum = nonZero.reduce((a, b) => {
return a + b;
}, 0);
return sum / nonZero.length;
};
/**
* Find the (planar) centroid of a set of points
* @param {Array} items list of location-like items having { lat, lng }
* @return {Object} object with averaged lat/lng
*/
export const centroid = (items) => ({
lat: arrayMean(items.map((item) => item.lat)),
lng: arrayMean(items.map((item) => item.lng)),
});
/**
* Returns a gaussian (normal) random function with the given mean and stdev.
* @param {Number} mean center value
* @param {Number} stdev standard deviation (radius around mean)
* @return {Function} function generating numbers with a normal distribution
*/
export function gaussian(mean, stdev, random = Math.random) {
let y2;
let use_last = false;
return () => {
let y1;
if (use_last) {
y1 = y2;
use_last = false;
} else {
let x1, x2, w;
do {
x1 = 2.0 * random() - 1.0;
x2 = 2.0 * random() - 1.0;
w = x1 * x1 + x2 * x2;
} while (w >= 1.0);
w = Math.sqrt((-2.0 * Math.log(w)) / w);
y1 = x1 * w;
y2 = x2 * w;
use_last = true;
}
return mean + stdev * y1;
// if (retval > 0) return retval;
// return -retval;
};
}
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