I'm trying to implement a simple Lotka-Volterra system in JavaScript, but get different result from what I see in academic papers and slides. This is my equations:
sim2.eval("dxdt(x, y) = (2 * x) - (x * y)");
sim2.eval("dydt(x, y) = (-0.25 * y) + (x * y)");
using coefficients a = 2, b = 1, c = 0.25 and d = 1. Yet, my result looks like this:
when I expected a stable oscillation as seen in these PDF slides:
Could it be the implementation of ndsolve that causes this? Or a machine error in JavaScript due to floating-point arithmetic?
Disregard, the error was simply using a too big evaluation step (dt = 0.1, must be 0.01 at least). The numerical method used is known for this problem.
For serious purposes use a higher order method, the minimum is fixed step classical Runge-Kutta. Then you can also use dt=0.1, it is stable for multiple periods, I tried tfinal=300 without problems. However you will see the step size in the graph as it is visibly piecewise linear. This is much reduced with half the step size, dt=0.05.
function odesolveRK4(f, x0, dt, tmax) {
var n = f.size()[0]; // Number of variables
var x = x0.clone(),xh=[]; // Current values of variables
var dxdt = [], k1=[], k2=[], k3=[], k4=[]; // Temporary variable to hold time-derivatives
var result = []; // Contains entire solution
var nsteps = math.divide(tmax, dt); // Number of time steps
dt2 = math.divide(dt,2);
dt6 = math.divide(dt,6);
for(var i=0; i<nsteps; i++) {
// compute the 4 stages if the classical order-4 Runge-Kutta method
k1 = f.map(function(fj) {return fj.apply(null, x.toArray()); } );
xh = math.add(x, math.multiply(k1, dt2));
k2 = f.map(function(fj) {return fj.apply(null, xh.toArray()); } );
xh = math.add(x, math.multiply(k2, dt2));
k3 = f.map(function(fj) {return fj.apply(null, xh.toArray()); } );
xh = math.add(x, math.multiply(k3, dt));
k4 = f.map(function(fj) {return fj.apply(null, xh.toArray()); } );
x = math.add(x, math.multiply(math.add(math.add(k1,k4), math.multiply(math.add(k2,k3),2)), dt6))
if( 0==i%50) console.log("%3d %o %o",i,dt,x.toString());
result.push(x.clone());
}
return math.matrix(result);
}
math.import({odesolveRK4:odesolveRK4});
I was just going through the source of vivus.js and came across the followng like of code:
currentFrame = this.animTimingFunction(this.currentFrame / this.frameLength) * this.frameLength;
Now this function call can be seen HERE.
The only other place this is defined in is below:
this.animTimingFunction = options.animTimingFunction || Vivus.LINEAR;
This can be seen on the repo HERE.
Now my question is , why is this.animTimingFunction being called as a function when it actually is not a function ? can anybody explain ?
Thank you.
But it is a function as mentioned in the code comments
animTimingFunction <function> timing animation function for the complete SVG`
From the code it is one of the options that can be passed to the Vivus constructor. Predefined timing functions are defined at line 66
/**
* Timing functions
**************************************
*
* Default functions to help developers.
* It always take a number as parameter (between 0 to 1) then
* return a number (between 0 and 1)
*/
Vivus.LINEAR = function (x) {return x;};
Vivus.EASE = function (x) {return -Math.cos(x * Math.PI) / 2 + 0.5;};
Vivus.EASE_OUT = function (x) {return 1 - Math.pow(1-x, 3);};
Vivus.EASE_IN = function (x) {return Math.pow(x, 3);};
Vivus.EASE_OUT_BOUNCE = function (x) {
var base = -Math.cos(x * (0.5 * Math.PI)) + 1,
rate = Math.pow(base,1.5),
rateR = Math.pow(1 - x, 2),
progress = -Math.abs(Math.cos(rate * (2.5 * Math.PI) )) + 1;
return (1- rateR) + (progress * rateR);
};
On line 204
this.animTimingFunction = options.animTimingFunction || Vivus.LINEAR;
you can see that it either uses the passed function or when nothing is set for animTimingFunction a default function defined at Vivus.LINEAR
So you can not pass a function, pass one of the predefined functions, or pass your own timing function:
Vivus(...,{},...);
//OR
Vivus(...,{
animTimingFunction:Vivus.EASE
},...);
//OR
Vivus(...,{
animTimingFunction:Vivus.EASE_OUT
},...);
//OR
Vivus(...,{
//custom function
//input number between 0 and 1
//output number between 0 and 1
animTimingFunction:function(x){
//manipulate x as needed and return the new number
}
},...);
I'm trying to figure out why my Google Chrome console is giving me the error "undefined is not a function." I have a hunch, but maybe I'm on the wrong track. My function boxCollision(...) is defined at the bottom of my class. Nearer to the top I have a statement
if (this.boxCollision(this.food.getBBox(), this.body[0].getBBox()))
this.food.translate(this.linkSize, 0);
the first line of which is causing the error I mentioned. I think that's maybe because I haven't yet defined boxCollision, so it's essentially nonexistent. Is that right? The getBBox() functions are recognized because they're from an external JavaScript file.
function snakegame(C, C_w, C_h, spd)
{
/* NOTE TO SELF: C is a Raphel object. Can't find a method to return the height
and width of a Raphael object in the documentation:
http://raphaeljs.com/reference.html#Raphael.
Using C_h and C_w for now, but should probably change it later.
*/
this.linkSize = 50; /* size of a snake unit, in pixels; must divide C_h and C_w */
this.link = C.rect(C_h/2, C_w/2, this.linkSize, this.linkSize);
this.link.attr("fill", "#E9E581");
this.body = [this.link];
this.food = C.rect(randInt(0,C_w/this.linkSize-1) * this.linkSize, randInt(0,C_h/this.linkSize-1) * this.linkSize, this.linkSize, this.linkSize);
if (this.boxCollision(this.food.getBBox(), this.body[0].getBBox()))
this.food.translate(this.linkSize, 0);
this.food.attr("fill","#B43535");
this.maxSnakeSize = C_h * C_w / (this.linkSize * this.linkSize);
/* On instantiation, the snake direction is down and has 1 link */
this.dy = 0;
this.dx = 0;
this.score = 0;
/* Event listener for changing the direction of the
snake with arroy keys on the keyboard
*/
this.redirect = function(dirnum)
{
switch (dirnum)
{
/*
dirnum corresponds to
1 ---> right
2 ---> down
3 ---> left
4 ---> up
*/
case 1:
this.dx = this.linkSize;
this.dy = 0;
break;
case 2:
this.dx = 0;
this.dy = this.linkSize;
break;
case 3:
this.dx = -this.linkSize;
this.dy = 0;
break;
case 4:
this.dx = 0;
this.dy = -this.linkSize;
break;
default: /* never happens */
break;
}
}
this.move = function()
{
if (this.body.length == this.maxSnakeSize)
{
this.destruct();
return;
}
var addLink = false;
var BBhead = this.body[0].getBBox();
if (this.hitWall(BBhead) || this.hitSnake(BBhead))
{
document.getElementById("snakescorediv").innerHTML = "<p>GAME OVER!</p><p>Score: "+ this.score +"</p>";
this.destruct();
return;
}
var BBfood = this.food.getBBox();
if (this.boxCollision(BBhead, BBfood))
{
this.moveFood();
this.score += 10;
document.getElementById("snakescorediv").innerHTML = this.score.toString();
addLink = true;
}
if (addLink)
this.body.push(this.body[this.body.length - 1].clone());
for (var i = this.body.length - 1; i > 0; --i)
{
var prevBB = this.body[i-1].getBBox();
var thisBB = this.body[i].getBBox();
this.body[i].translate(prevBB.x-thisBB.x, prevBB.y-thisBB.y)
}
this.body[0].translate(this.dx, this.dy);
}
this.mover = setInterval(this.move.bind(this), spd);
this.hitWall = function(bb)
{
return bb.x < 0 || bb.x2 > C_w || bb.y < 0 || bb.y2 > C_h;
}
this.hitSnake = function(bb)
{
var retval = false;
for (var i = 1, j = this.body.length; i < j; ++i)
{
var thisbb = this.body[i].getBBox();
if (this.boxCollision(bb, thisbb))
{
retval = true;
break;
}
}
return retval;
}
this.moveFood = function()
{
var bbf = this.food.getBBox(); // bounding box for food
do {
/* tx, ty: random translation units */
tx = randInt(0, C_w / this.linkSize - 1) * this.linkSize - bbf.x;
ty = randInt(0, C_h / this.linkSize - 1) * this.linkSize - bbf.y;
// translate copy of food
this.food.translate(tx, ty);
bbf = this.food.getBBox(); // update bbf
} while (this.hitSnake(bbf));
}
this.boxCollision = function(A, B)
{
return A.x == B.x && A.y == B.y;
}
this.destruct = function()
{
clearInterval(this.mover);
for (var i = 0, j = this.body.length; i < j; ++i)
{
this.body[i].removeData();
this.body[i].remove();
}
this.food.removeData();
this.food.remove();
this.score = 0;
}
}
Put the methods on the prototype to avoid this issue.
This won't work:
function Ctor() {
this.init()
this.init = function() {
console.log('init')
}
}
var inst = new Ctor // Error: undefined is not a function
But this will:
function Ctor() {
this.init()
}
Ctor.prototype.init = function() {
console.log('init')
}
var inst = new Ctor // init
Javascript parses code in two steps: compilation and evaluation.
The first step is compilation. In this step all definitions are compiled but no statement or expressions are evaluated. What this means is that definitions such as:
function a () {}
and:
var x
gets compiled into memory.
In the evaluation phase the javascript interpreter finally starts executing. This allows it to process operators which makes it possible to execute statements and expressions. It is in this step that variables get their values:
var x = 10;
^ ^
| |______ this part now gets assigned to `x` in the evaluation phase
|
this part was processed in the compilation phase
What this means is that for function expressions:
var x = function () {}
while both the variable and function body are compiled in the compilation phase, the anonymous function is not assigned to the variable until the evaluation phase. That's because the = operator is only executed in the evaluation phase (during the compilation phase all variables are allocated memory and assigned the value undefined).
Both the compilation phase and evaluation phase happen strictly top-down.
What some call "hoisting" is simply the fact that the compilation phase happen before the evaluation phase.
One work-around is to simply use a function definition instead of a function expression. Javascript support inner functions so a function defined in another function doesn't exist in the global scope:
function boxCollision (A, B) {
return A.x == B.x && A.y == B.y;
}
this.boxCollision = boxCollision;
Then you can use it at the top of your constructor:
if (boxCollision(this.food.getBBox(), this.body[0].getBBox()))
this.food.translate(this.linkSize, 0);
Note that you can't use this.boxCollision because it's still undefined when you call it.
Another obvious work-around is to of course assign this.boxCollision = function (){} at the top before using it.
Or you could even assign it to the constructor's prototype. Or you can have an init function that gets called at the top (note: function, not method - again the use of a definition instead of a function expression make use of "hoisting").
There are many ways to get around this. But it's useful to know why it's happening to understand what works and what doesn't.
See my answer to this related question for more examples of this behavior: JavaScript function declaration and evaluation order
Can I write a JavaScript function from scratch that behaves like Math.random?
(By that I mean without using Math.random.)
Yes you can, you can implement your own LCG number generator, but as Sarnold mentions you need to maintain state between calls.
Per #OscarGomez's answer regarding a linear congruential generator, here's an example of a random number generator as a plain JavaScript function. Of course, its quality of "randomness" (currently very poor due to a short cycle) appears to be dependent on picking good values for the constants in the enclosed object "o".
var random = (function() {
var o = {mod: 13, mul: 11, inc: 7, x: 0};
return function() {
return o.x = (o.mul * o.x + o.inc) % o.mod
}
})();
random(); // => 7
random(); // => 6
random(); // => 8
random(); // => 4
Here's a more portable version which can have separate generator instances and seeds:
function Random(s) {
this.seed = s || 0;
this.mod = 13;
this.mul = 11;
this.inc = 7;
this.x = this.seed;
}
Random.prototype.next = function() {
return (this.x = (this.mul * this.x + this.inc) % this.mod);
};
var r = new Random(1);
r.next(); // => 5
r.next(); // => 10
r.next(); // => 7
What I usually do when I need some randomness but am to lazy to look up the syntax is to implement the logistic map (a discrete chaotic system). In pseudo code this is like this:
var x = 0.234; // or some other number between 0 and 1 ( but not 0.5 )
for (var n=1; n<=100;n++){
x = 4 * x * (1-x); // this is the iteration
console.log(x);
}
This would print 100 somehow random numbers, not really random but for many situations random enough.
Sorry for not giving a javascript answer, I havent used that for a decade.
The JavaScript Math.random() function returns a random value between 0 and 1, automatically seeded based on the current time (similar to Java I believe). However, I don't think there's any way to set you own seed for it.
How can I make a random number generator that I can provide my own seed value for, so that I can have it produce a repeatable sequence of (pseudo)random numbers?
One option is http://davidbau.com/seedrandom which is a seedable RC4-based Math.random() drop-in replacement with nice properties.
If you don't need the seeding capability just use Math.random() and build helper functions around it (eg. randRange(start, end)).
I'm not sure what RNG you're using, but it's best to know and document it so you're aware of its characteristics and limitations.
Like Starkii said, Mersenne Twister is a good PRNG, but it isn't easy to implement. If you want to do it yourself try implementing a LCG - it's very easy, has decent randomness qualities (not as good as Mersenne Twister), and you can use some of the popular constants.
EDIT: consider the great options at this answer for short seedable RNG implementations, including an LCG option.
function RNG(seed) {
// LCG using GCC's constants
this.m = 0x80000000; // 2**31;
this.a = 1103515245;
this.c = 12345;
this.state = seed ? seed : Math.floor(Math.random() * (this.m - 1));
}
RNG.prototype.nextInt = function() {
this.state = (this.a * this.state + this.c) % this.m;
return this.state;
}
RNG.prototype.nextFloat = function() {
// returns in range [0,1]
return this.nextInt() / (this.m - 1);
}
RNG.prototype.nextRange = function(start, end) {
// returns in range [start, end): including start, excluding end
// can't modulu nextInt because of weak randomness in lower bits
var rangeSize = end - start;
var randomUnder1 = this.nextInt() / this.m;
return start + Math.floor(randomUnder1 * rangeSize);
}
RNG.prototype.choice = function(array) {
return array[this.nextRange(0, array.length)];
}
var rng = new RNG(20);
for (var i = 0; i < 10; i++)
console.log(rng.nextRange(10, 50));
var digits = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'];
for (var i = 0; i < 10; i++)
console.log(rng.choice(digits));
If you want to be able to specify the seed, you just need to replace the calls to getSeconds() and getMinutes(). You could pass in an int and use half of it mod 60 for the seconds value and the other half modulo 60 to give you the other part.
That being said, this method looks like garbage. Doing proper random number generation is very hard. The obvious problem with this is that the random number seed is based on seconds and minutes. To guess the seed and recreate your stream of random numbers only requires trying 3600 different second and minute combinations. It also means that there are only 3600 different possible seeds. This is correctable, but I'd be suspicious of this RNG from the start.
If you want to use a better RNG, try the Mersenne Twister. It is a well tested and fairly robust RNG with a huge orbit and excellent performance.
EDIT: I really should be correct and refer to this as a Pseudo Random Number Generator or PRNG.
"Anyone who uses arithmetic methods to produce random numbers is in a state of sin."
--- John von Neumann
I use a JavaScript port of the Mersenne Twister:
https://gist.github.com/300494
It allows you to set the seed manually. Also, as mentioned in other answers, the Mersenne Twister is a really good PRNG.
The code you listed kind of looks like a Lehmer RNG. If this is the case, then 2147483647 is the largest 32-bit signed integer, 2147483647 is the largest 32-bit prime, and 48271 is a full-period multiplier that is used to generate the numbers.
If this is true, you could modify RandomNumberGenerator to take in an extra parameter seed, and then set this.seed to seed; but you'd have to be careful to make sure the seed would result in a good distribution of random numbers (Lehmer can be weird like that) -- but most seeds will be fine.
The following is a PRNG that may be fed a custom seed. Calling SeedRandom will return a random generator function. SeedRandom can be called with no arguments in order to seed the returned random function with the current time, or it can be called with either 1 or 2 non-negative inters as arguments in order to seed it with those integers. Due to float point accuracy seeding with only 1 value will only allow the generator to be initiated to one of 2^53 different states.
The returned random generator function takes 1 integer argument named limit, the limit must be in the range 1 to 4294965886, the function will return a number in the range 0 to limit-1.
function SeedRandom(state1,state2){
var mod1=4294967087
var mul1=65539
var mod2=4294965887
var mul2=65537
if(typeof state1!="number"){
state1=+new Date()
}
if(typeof state2!="number"){
state2=state1
}
state1=state1%(mod1-1)+1
state2=state2%(mod2-1)+1
function random(limit){
state1=(state1*mul1)%mod1
state2=(state2*mul2)%mod2
if(state1<limit && state2<limit && state1<mod1%limit && state2<mod2%limit){
return random(limit)
}
return (state1+state2)%limit
}
return random
}
Example use:
var generator1=SeedRandom() //Seed with current time
var randomVariable=generator1(7) //Generate one of the numbers [0,1,2,3,4,5,6]
var generator2=SeedRandom(42) //Seed with a specific seed
var fixedVariable=generator2(7) //First value of this generator will always be
//1 because of the specific seed.
This generator exhibit the following properties:
It has approximately 2^64 different possible inner states.
It has a period of approximately 2^63, plenty more than anyone will ever realistically need in a JavaScript program.
Due to the mod values being primes there is no simple pattern in the output, no matter the chosen limit. This is unlike some simpler PRNGs that exhibit some quite systematic patterns.
It discards some results in order to get a perfect distribution no matter the limit.
It is relatively slow, runs around 10 000 000 times per second on my machine.
Bonus: typescript version
If you program in Typescript, I adapted the Mersenne Twister implementation that was brought in Christoph Henkelmann's answer to this thread as a typescript class:
/**
* copied almost directly from Mersenne Twister implementation found in https://gist.github.com/banksean/300494
* all rights reserved to him.
*/
export class Random {
static N = 624;
static M = 397;
static MATRIX_A = 0x9908b0df;
/* constant vector a */
static UPPER_MASK = 0x80000000;
/* most significant w-r bits */
static LOWER_MASK = 0x7fffffff;
/* least significant r bits */
mt = new Array(Random.N);
/* the array for the state vector */
mti = Random.N + 1;
/* mti==N+1 means mt[N] is not initialized */
constructor(seed:number = null) {
if (seed == null) {
seed = new Date().getTime();
}
this.init_genrand(seed);
}
private init_genrand(s:number) {
this.mt[0] = s >>> 0;
for (this.mti = 1; this.mti < Random.N; this.mti++) {
var s = this.mt[this.mti - 1] ^ (this.mt[this.mti - 1] >>> 30);
this.mt[this.mti] = (((((s & 0xffff0000) >>> 16) * 1812433253) << 16) + (s & 0x0000ffff) * 1812433253)
+ this.mti;
/* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
/* In the previous versions, MSBs of the seed affect */
/* only MSBs of the array mt[]. */
/* 2002/01/09 modified by Makoto Matsumoto */
this.mt[this.mti] >>>= 0;
/* for >32 bit machines */
}
}
/**
* generates a random number on [0,0xffffffff]-interval
* #private
*/
private _nextInt32():number {
var y:number;
var mag01 = new Array(0x0, Random.MATRIX_A);
/* mag01[x] = x * MATRIX_A for x=0,1 */
if (this.mti >= Random.N) { /* generate N words at one time */
var kk:number;
if (this.mti == Random.N + 1) /* if init_genrand() has not been called, */
this.init_genrand(5489);
/* a default initial seed is used */
for (kk = 0; kk < Random.N - Random.M; kk++) {
y = (this.mt[kk] & Random.UPPER_MASK) | (this.mt[kk + 1] & Random.LOWER_MASK);
this.mt[kk] = this.mt[kk + Random.M] ^ (y >>> 1) ^ mag01[y & 0x1];
}
for (; kk < Random.N - 1; kk++) {
y = (this.mt[kk] & Random.UPPER_MASK) | (this.mt[kk + 1] & Random.LOWER_MASK);
this.mt[kk] = this.mt[kk + (Random.M - Random.N)] ^ (y >>> 1) ^ mag01[y & 0x1];
}
y = (this.mt[Random.N - 1] & Random.UPPER_MASK) | (this.mt[0] & Random.LOWER_MASK);
this.mt[Random.N - 1] = this.mt[Random.M - 1] ^ (y >>> 1) ^ mag01[y & 0x1];
this.mti = 0;
}
y = this.mt[this.mti++];
/* Tempering */
y ^= (y >>> 11);
y ^= (y << 7) & 0x9d2c5680;
y ^= (y << 15) & 0xefc60000;
y ^= (y >>> 18);
return y >>> 0;
}
/**
* generates an int32 pseudo random number
* #param range: an optional [from, to] range, if not specified the result will be in range [0,0xffffffff]
* #return {number}
*/
nextInt32(range:[number, number] = null):number {
var result = this._nextInt32();
if (range == null) {
return result;
}
return (result % (range[1] - range[0])) + range[0];
}
/**
* generates a random number on [0,0x7fffffff]-interval
*/
nextInt31():number {
return (this._nextInt32() >>> 1);
}
/**
* generates a random number on [0,1]-real-interval
*/
nextNumber():number {
return this._nextInt32() * (1.0 / 4294967295.0);
}
/**
* generates a random number on [0,1) with 53-bit resolution
*/
nextNumber53():number {
var a = this._nextInt32() >>> 5, b = this._nextInt32() >>> 6;
return (a * 67108864.0 + b) * (1.0 / 9007199254740992.0);
}
}
you can than use it as follows:
var random = new Random(132);
random.nextInt32(); //return a pseudo random int32 number
random.nextInt32([10,20]); //return a pseudo random int in range [10,20]
random.nextNumber(); //return a a pseudo random number in range [0,1]
check the source for more methods.
Here is quite an effective but simple javascript PRNG function that I like to use:
// The seed is the base number that the function works off
// The modulo is the highest number that the function can return
function PRNG(seed, modulo) {
str = `${(2**31-1&Math.imul(48271,seed))/2**31}`
.split('')
.slice(-10)
.join('') % modulo
return str
}
I hope this is what you're looking for.
Thank you, #aaaaaaaaaaaa (Accepted Answer)
I really needed a good non-library solution (easier to embed)
so... i made this class to store the seed and allow a Unity-esque "Next" ... but kept the initial Integer based results
class randS {
constructor(seed=null) {
if(seed!=null) {
this.seed = seed;
} else {
this.seed = Date.now()%4645455524863;
}
this.next = this.SeedRandom(this.seed);
this.last = 0;
}
Init(seed=this.seed) {
if (seed = this.seed) {
this.next = this.SeedRandom(this.seed);
} else {
this.seed=seed;
this.next = this.SeedRandom(this.seed);
}
}
SeedRandom(state1,state2){
var mod1=4294967087;
var mod2=4294965887;
var mul1=65539;
var mul2=65537;
if(typeof state1!="number"){
state1=+new Date();
}
if(typeof state2!="number"){
state2=state1;
}
state1=state1%(mod1-1)+1;
state2=state2%(mod2-1)+1;
function random(limit){
state1=(state1*mul1)%mod1;
state2=(state2*mul2)%mod2;
if(state1<limit && state2<limit && state1<mod1%limit && state2<mod2%limit){
this.last = random;
return random(limit);
}
this.last = (state1+state2)%limit;
return (state1+state2)%limit;
}
this.last = random;
return random;
}
}
And then checked it with these... seems to work well with random (but queryable) seed value (a la Minecraft) and even stored the last value returned (if needed)
var rng = new randS(9005646549);
console.log(rng.next(20)+' '+rng.next(20)+' '+rng.next(20)+' '+rng.next(20)+' '+rng.next(20)+' '+rng.next(20)+' '+rng.next(20));
console.log(rng.next(20) + ' ' + rng.next(20) + ' ' + rng.last);
which should output (for everybody)
6 7 8 14 1 12 6
9 1 1
EDIT: I made the init() work if you ever needed to reseed, or were testing values (this was necessary in my context as well)
Note: This code was originally included in the question above. In the interests of keeping the question short and focused, I've moved it to this Community Wiki answer.
I found this code kicking around and it appears to work fine for getting a random number and then using the seed afterward but I'm not quite sure how the logic works (e.g. where the 2345678901, 48271 & 2147483647 numbers came from).
function nextRandomNumber(){
var hi = this.seed / this.Q;
var lo = this.seed % this.Q;
var test = this.A * lo - this.R * hi;
if(test > 0){
this.seed = test;
} else {
this.seed = test + this.M;
}
return (this.seed * this.oneOverM);
}
function RandomNumberGenerator(){
var d = new Date();
this.seed = 2345678901 + (d.getSeconds() * 0xFFFFFF) + (d.getMinutes() * 0xFFFF);
this.A = 48271;
this.M = 2147483647;
this.Q = this.M / this.A;
this.R = this.M % this.A;
this.oneOverM = 1.0 / this.M;
this.next = nextRandomNumber;
return this;
}
function createRandomNumber(Min, Max){
var rand = new RandomNumberGenerator();
return Math.round((Max-Min) * rand.next() + Min);
}
//Thus I can now do:
var letters = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'];
var numbers = ['1','2','3','4','5','6','7','8','9','10'];
var colors = ['red','orange','yellow','green','blue','indigo','violet'];
var first = letters[createRandomNumber(0, letters.length)];
var second = numbers[createRandomNumber(0, numbers.length)];
var third = colors[createRandomNumber(0, colors.length)];
alert("Today's show was brought to you by the letter: " + first + ", the number " + second + ", and the color " + third + "!");
/*
If I could pass my own seed into the createRandomNumber(min, max, seed);
function then I could reproduce a random output later if desired.
*/
OK, here's the solution I settled on.
First you create a seed value using the "newseed()" function. Then you pass the seed value to the "srandom()" function. Lastly, the "srandom()" function returns a pseudo random value between 0 and 1.
The crucial bit is that the seed value is stored inside an array. If it were simply an integer or float, the value would get overwritten each time the function were called, since the values of integers, floats, strings and so forth are stored directly in the stack versus just the pointers as in the case of arrays and other objects. Thus, it's possible for the value of the seed to remain persistent.
Finally, it is possible to define the "srandom()" function such that it is a method of the "Math" object, but I'll leave that up to you to figure out. ;)
Good luck!
JavaScript:
// Global variables used for the seeded random functions, below.
var seedobja = 1103515245
var seedobjc = 12345
var seedobjm = 4294967295 //0x100000000
// Creates a new seed for seeded functions such as srandom().
function newseed(seednum)
{
return [seednum]
}
// Works like Math.random(), except you provide your own seed as the first argument.
function srandom(seedobj)
{
seedobj[0] = (seedobj[0] * seedobja + seedobjc) % seedobjm
return seedobj[0] / (seedobjm - 1)
}
// Store some test values in variables.
var my_seed_value = newseed(230951)
var my_random_value_1 = srandom(my_seed_value)
var my_random_value_2 = srandom(my_seed_value)
var my_random_value_3 = srandom(my_seed_value)
// Print the values to console. Replace "WScript.Echo()" with "alert()" if inside a Web browser.
WScript.Echo(my_random_value_1)
WScript.Echo(my_random_value_2)
WScript.Echo(my_random_value_3)
Lua 4 (my personal target environment):
-- Global variables used for the seeded random functions, below.
seedobja = 1103515.245
seedobjc = 12345
seedobjm = 4294967.295 --0x100000000
-- Creates a new seed for seeded functions such as srandom().
function newseed(seednum)
return {seednum}
end
-- Works like random(), except you provide your own seed as the first argument.
function srandom(seedobj)
seedobj[1] = mod(seedobj[1] * seedobja + seedobjc, seedobjm)
return seedobj[1] / (seedobjm - 1)
end
-- Store some test values in variables.
my_seed_value = newseed(230951)
my_random_value_1 = srandom(my_seed_value)
my_random_value_2 = srandom(my_seed_value)
my_random_value_3 = srandom(my_seed_value)
-- Print the values to console.
print(my_random_value_1)
print(my_random_value_2)
print(my_random_value_3)