utilities.js

/********* Utility functions ************//*
These are mostly mathematical utilities. 
I like matrices so I wanna be able to use them.
*//***************************************/

function enumerate(input) {
    /*
    INPUT
    a: a list of values to permute
    RETURN
    o: an array of all permutations
    e.g. a = [2,2] --> o = [[0,0],[0,1],[1,0],[1,1]]
    */
    o = new Array(product(input));
    for (var i=0; i<o.length; i++) {
        x = i;
        o[i] = new Array(input.length);
        for (var j=input.length-1; j>=0; j--) {
            o[i][j] = x%input[j];
            x = Math.floor(x/input[j]);
        }
    }
    return o;
}

function product(input) {
	var p = 1;
	for (var i=0; i<input.length; i++) { p *= input[0]; }
	return p;
}

function sum(input) {
	var s = 1;
	for (var i=0; i<input.length; i++) { s += input[0]; }
	return s;
}

function not(input) {
	/* input is either scalar or matrix-like array. returns array of same size as input with elements that evaluate to true replaced with 0 and false replaced with 1 */
	if (!(input instanceof Array)) {
		return (input) ? (0) : (1);
	}
	else
	{
		var o = [];
		for (var i=0; i<input.length; i++) {
			o[i] = not(input[i]);
		}
		return o;
	}
}

function ones_like(mat) {
	// assume mat 2D matrix-like array
	var out = [];
	for (var i=0; i<mat.length; i++){
		if (mat[i] instanceof Array) {
			for (var j=0; j<mat[i].length; j++){
				out[i][j] = 1;
			}
		}
		else {
			out[i] = 1;
		}
	}
	return out;
}

function find(mat) {
	//input assumed to be 2D matrix-like array. returns indices of elements that evaluate to true 

	var indices = [];

	for (var i=0; i<mat.length; i++){
		for (var j=0; j<mat[i].length; j++){
			if (mat[i][j]) {indices.push([i,j]);}
		}
	}
	return indices;
}

function random_elements(list, n, replacement, distribution) {
	// input is a list-like array. returns a random element of list. uniform distribution.
	var o = [];
	replacement = replacement || false;

		for (var i=0; i<n; i++){
			var index = Math.floor(Math.random()*list.length);
			o.push(list[index]);
			if (!replacement){
				list.splice(index,1);
			}
		}
	return o;
}