I discovered this when I wanted to make deterministic random vectors and matrices. To get the same result from each entry on every access, I can either cache the values or use an algorithm to recreate unique seed for that entry. I naively just added the coordinate to the base seed, and created very not-random vectors and matrices. Yes, the JDK Random is intended to be lame but fast., but this was just too far over the line.
Lance On Sun, Feb 20, 2011 at 2:31 AM, Dawid Weiss <[email protected]> wrote: > A perhaps better question is what are you trying to prove or what was > your original intention? :) This is a very strange program indeed -- > what it does is basically check what the next double value from a > fixed initial seed is... since random uses a relatively simple > congruential algorithm, the result isn't really that surprising (to > me?). > > Dawid > > On Sun, Feb 20, 2011 at 2:51 AM, Lance Norskog <[email protected]> wrote: >> What does this program print? >> >> >> package hack; >> >> import java.util.Random; >> >> public class JDKRandomThreatOrMenace { >> >> public static void main(String[] args) { >> Random rnd = new Random(0); >> >> double last = rnd.nextDouble(); >> long i = 1; >> for(; i < Long.MAX_VALUE; i++) { >> rnd.setSeed(i); >> double next = rnd.nextDouble(); >> if (Math.abs(next - last) > 0.2) >> break; >> } >> System.out.println(i); >> } >> >> } >> >> Your prize if you get it right? A patch would be welcome... >> >> > -- Lance Norskog [email protected]
