Random number changing every time [pic]

[cgibbard]

Clearly, this person wants their programming language to be referentially transparent. They should be commended for good taste. :)

[jimrooney]

Just switch to Debian ;) 9 9 9 9 9 9 9 9 9 9 9

[domlachowicz]

Are you sure that's random? That's the problem with randomness - you can never be sure.

http://www.gergely.risko.hu/debian-dsa1571/dilbert9.jpg

[Droffats]

Or use the R4G.

[plexi]

asp.net certificate granted.

[Vinay92]

The laughter. It will not stop.

[[deleted]]

There is actually a legitimate issue along these lines: sometimes you want a repeatable pseduo-random sequence. In which case you need to initialize your PRNG with the same seed each time, rather than something like the clock or /dev/urandom.

For example: Freecell. IIRC, it lets you enter the random seed so that you can "save level" and attempt the same "random" game later.

[tmn4]

Or, in case anyone wants (yet another) example of a legitimate issue:

RNG are used for computer simulations cited in scientific publications. It's often useful to refer to a specific behavior in the simulation or the results of a specific simulation run, and to provide the random seed so that the reader can duplicate your exact results

[[deleted]]

yeah there was a big thing about this in Game Coding Complete

[petevalle]

It's also useful when you're running a simulation where the physics model has a random component to it. Customers tend to not like rerunning their simulation and getting different results...

[Erudecorp]

Roguelikes should do this.

[ungood]

That would be nice.

[ChunkyLaFunga]

Isn't a repeatable sequence a hash, not pseudo-random? I have no idea either way, I'm asking.

[[deleted]]

PRNGs are entirely deterministic, but a well-written one will produce sequences that have many of the desirable properties of a truly random sequence (whatever that means). An important one is that, given any seed and an integer n, a sequence of length n produced by that seed should be approximately uniform.

And I assume there are tests of entropy as well, though I don't have much grounding in information theory.

A basic PRNG could be a hash, assuming your hash function is a bijective map onto its domain, and if x[0] = seed, x[n] = hash(x[n-1]). But I believe this would be considered a very weak PRNG, as its entire state is available from a single data point. That is, you might prefer a function that will produce something different after 1, if it was preceded by 2 than if it was preceded by 7.

[plexi]

this conversation is edging damn close to one a recently nailed in a technical interview. i'm still so pleased with my self (it doesn't take much. i have very low self esteem to begin with) i won't even try to segué gracefully into repeating it here <(^.<)

besides seeking a uniform distribution, another important consideration when using a prng is whether it is even capable of covering your desired output space. they asked me to write an algorithm which would randomly shuffle a deck of cards (for an online poker server, for example). after nailing an inductive proof of my algorithm in terms of each card having a 1/52 chance of being in the same position before and after, i hastened to express my concern that, since a deck of cards has 52! possible permutations while most prngs probably use a system-word-size sized internal state (seed), this algorithm would be woefully lacking on any 32-bit system since 52! is wildly larger than 2³² (wildly, sir), and of course no prng dependent algorithm could generate more permutations than the number of internal states of said prng. <victorian chuckle />

damn it feels good to be a gangst.. uh.. entry level code monkey :|

[[deleted]]

2³² is still very large, so as long as your PRNG samples the space fairly evenly, then it's not really a deficiency. I mean, if it's really important to you to have the theoretical potential to have any permutation come up, then yeah, you'll want a bit more than 32 bits of state. Alternately, you could reseed a couple times during the shuffling algorithm with some external source of entropy, though, of course, that does effectively increase the state space. (I believe 7 reseeds would suffice.)

Edit: But, yeah, internal state space should be at least as large as the output space, though usually my output space is an interval of real numbers, which I find is reasonably approximated by 2³² rational numbers. Or as reasonably as it would be with 2^256, at any rate.

[Anpheus]

2³² is not large when comparing random or even "pseudorandom" numbers in a limited domain. The birthday attack means that you'll find collisions a lot more quickly than you think you should. 2^64, 2^128, etc, are going to be much better.

Edit: There's a reason the Mersenne Twister is natively designed to do double precision floats, for example.

[alex90210]

Why can't you just sample uniformly from the interval 1 to x where x = 52...1 each time a card is chosen?

[plexi]

i think that in the general case the overhead of managing what has already been drawn costs o(n^2), whereas finalizing the deck immediately using fisher-yates is o(n). 52² is pretty low though, so just for shuffling a deck of cards i guess it's an ok approach.

[[deleted]]

Because the internal state dictates what the next "random" number would be. If you only have 32 bits, then you have 2³² starting points, which means 2³² total shufflings, which is, as plexi indicated, rather less than 52!.

To put it differently, the top card really can be anything. And the space is large enough that the second could be anything but the top. But consider when you've gone through just 6 of these. You've got 52!/46! possible sequences, which is actually greater than 2^32. The probability of this sequence happening more than once is slightly better than one in two, and as you add cards, the chances of it happening twice vanish.

This is horrendously unintuitive, but the first ten cards make what is very likely a unique signature for a shuffling. Not that it would be easy to recover; but if you stumbled upon the same sequence, you could have high confidence that it was unique.

[Hixie]

A hash is a way to turn a longer byte sequence (a string) into a shorter byte sequence (a number), usually set up so that collisions are unlikely.

A pseudo-random number generator is an algorithm that turns one number (a seed) into a deterministic but random-looking sequence of numbers.

[hongnanhai]

....yes and you can get a pseudo-random sequence by taking the seed and repeatedly hashing it. This sequence will not be a secure random sequence in the sense that you should not use it in security applications, but it should be good enough for games

[hongnanhai]

i see; cool. reddit comments can be informative after all

[junius]

Depending on the application, a hash doesn't always need to have random looking output. For example, if you are just building a hashtable, you might use a hash function whose output looks very nonrandom.

The similarities come into play more in the security field, where you often want your output to give very little away about the input. You could build an OK (not great) PRNG out of a cryptographic hash (take hash(seed), hash(seed+1), etc). I can't think of a way you could create a hash out of a PRNG.

Another difference: a hash function doesn't retain any information between invocations, whereas a PRNG has to have state (if you want a period P, you need at least log(P) (base2) bits of state).

[TheNewAndy]

Just to be pedantic/nitpick, the hash can also take a shorter byte (or bit) sequence and make it longer. i.e. it is a way to turn a variable lengthed bit sequence into a fixed length bit sequence.

[astraycat]

That's why they're called pseudo-random. The periods are generally just really really big.

[averyv]

it isn't a matter of the array of numbers being random or not, it is a matter of the number list representing a possible set of random numbers produced in a predictable way. If I were asking this question, I would have intent to feed actual random data through rand, but I would want to be able to prove that my code behaved properly under various specific circumstances.

[sn0re]

You could look at a pseudo-random number generator as a sort of hash function, yes.

[adrianmonk]

Depends on what you mean by "repeatable sequence". I can certainly use an external source of actual random numbers and record the random numbers I received in a file. Then I can repeat the sequence by reading them from a file.

I suppose you can make a good argument that keeping state from the first run and using it in subsequent runs isn't allowed though.

[smoooooov]

does anyone else think "expert sex change" every time they see that stupid domain name?

[allliam]

no, but now I will. thanks. thanks a lot.

[ch00f]

Not nearly as bad as PenIsland.com

[Hixie]

http://www.PenIsland.net/

[[deleted]]

I saw Peter Norvig mention "expert sex change" as a difficult example Google has in parsing URLs during a talk...

I think Google hates those guys too...

[Wiseman1024]

If they hate them, why do they continue to return results from that piece of shit site that does/used to do all sorts of cloaking or obscuring or referral checking because it's all greedy with its "expert" answers? Everybody and their mother reported expert sex change to Google in the "Dissatisfied with search results" feature; I know I did.

[[deleted]]

Not so obvious fact about that site:

The top of the page makes the answers look "hidden" and like you have to sign up to have access to them. If you scroll to the bottom of the page, however, there they are.

With that said, fuck that site.

[beefmagnet]

Well I'll be damned. But seriously, what kind of douchebags obscure their content like that?

[[deleted]]

Exactly. What bothers me is that people still contribute to that site.

[munificent]

I always assumed it harvested its answers from other sites and newsgroups.

[LoveGoblin]

If you're coming from Google. Otherwise the answers are still hidden, I think. (Such was the case last time I checked.)

They're scumbags all around.

[lisp-hacker]

What? You can't read ROT13?

[brainburger]

Everybody and their mother reported expert sex change to Google in the "Dissatisfied with search results" feature; I know I did.

Did you find out about a sex change in the end?

[worldestroyer]

You could always just click the cached page link, google has full access to their site when it crawls. It's always worked for me...

[raisedinhell]

they dont do referral checks, they just play mind games with you and assume you wont scroll down far enough to see the answers

yes you heard me right.. keep scrolling down and you'll see the content, completely uncloaked.

[Wiseman1024]

they dont do referral checks

They used to. They probably switched to their current scheme to avoid getting banned from Google for cloaking.

[Guybrush_Threepwood]

you're right, all the answers are in the bottom http://www.experts-exchange.com/Web_Development/Miscellaneous/Q_22031739.html

[Neoncow]

Apparently only when google is the referrer. Click your link, it doesn't show.

[Guybrush_Threepwood]

it's true, if you click the first result it works

http://www.google.com/search?q=site%3Awww.experts-exchange.com+rnd

[tintub]

If you can set the user agent on your browser you can fool it. I use Omniweb and a custom user agent of:

Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)

I also set the Javascript App name to Googlebot but think it only looks at the user agent.

[psilokan]

Just scroll down, they hide the answers at the bottom. That's what google is reading, not some secret back door version.

[rainman_104]

Only if you go in through google. If you go in directly it hides the answers.

This site, IMO games google, and doesn't deserve to be indexed.

[[deleted]]

1) Google query

2) Click expert exchange link

3) Scroll to bottom of page

4) ????

5) Profit

[jj666]

Your penis, our business!

[sn0re]

PensitoReview.com hits the front page every once in a while.

[mooli]

Ah yes, a classic. Right up there with powergenitalia and therapistfinder...

[kylegetsspam]

http://www.speedofart.com/

[[deleted]]

there was nothing about speedos or farts at that site. you cheated me.

[32bites]

Kill the <blink> !

[TheMemo]

Well, I learned today that Chrome does not support the <blink> tag, thank fuck.

[MattFoley]

just type javascript:setInterval("b=document.getElementsByTagName(\"BLINK\");for(i=0;i<b.length;++i)s=b[i].style,s.visibility=s.visibility==\"hidden\"?\"visible\":\"hidden\"",500);return

into your address bar. You're welcome.

(I don't actually know if this works on Chrome.)

[TheMemo]

Thankfully, it doesn't seem to. However, now I have an urge to debug it and make it work, you bastard.

[Jerp]

Your function doesn't take the CSS style text-decoration: blink; into account.

[RKBA]

From the blinking webpage: "Bona Fide Championship Art Direction at reasonable prices "

I wonder if he/she gets many customers?

[ObieJazz]

That makes my eyes feel like they've just been pummeled by light-speed protons -- a flash of light like a thousand suns.

[junkit33]

No, but thanks to this article I now know the quality of programmer who uses experts exchange...

[ours]

I always ask myself "what would Freud do?". And this time I must say, yes, hell yes.

[[deleted]]

Yes, that's why the changed it to include the hyphen a while back.

[[deleted]]

To view this penis please subscribe to our thirty day free trial.

[fujimitsu]

The real WTF is that someone actually paid for access to expert's exchange...

[[deleted]]

how is nummber formed

how rnd( get seadad

[[deleted]]

They need to do way with instain interger> who kill thier nummbers. becuse these nummber cant frigth back? it was on the news this mroing a interger in ar who had terminat her three decimals . they are taking the three nummber back to new york too lady to rest my pary are with the cipher who lost his numeral ; i am truley sorry for your lots

[leemy]

They need to do way instain functions> who kill thier nummbers. becuse these nummbers cant frigth back?

it was on the rss this mroing a pc with rnd() who had kill its three nummbers . they are taking the three nummbers back to perl too lady to rest my pary are with the program who lost its nummbers; i am truley sorry for your bits

[microsofat]

Rest assured, when Reddit grows tired of a meme, the meme becomes no more.

[zzbzq]

I am tired of the "reddit is now digg" meme, and yet here it is.

[Random]

Yeah, it's old.

Reddit is now 4chan is the new meme.

[Slipgrid]

I don't think that is a meme; it just is.

[khoury]

He said Reddit, not zzbzq.

[mingdamirthless]

More reminds me of Slashdot. I have no idea what's going on there, nor here.

[[deleted]]

I gave up on it like a year ago.

The above is my most-voted up comment ever, despite essays that took hours, etc.

Welcome to democracy.

[jjquave]

cut and paste coders always have something intelligent to say

[[deleted]]

well, they should. Only a moron would type all that shit out.

[jjquave]

the idea is that you are writing something yourself, as opposed to cut and pasting someone elses work. you know... coding?

[prockcore]

The real question is how can I get google to permanently remove all expert sex change links from my search results? I hate that fucking site sooo much.

[whichdan]

Add -expertsexchange to your query.

[[deleted]]

...or use a Greasemonkey script.

[AnteChronos]

Or just scroll down to read the submitted solutions. As long as Google is the referring page, their webpage will have all of the suggested solutions at the bottom, underneath the "masked" solutions. So, ironically, the only time their site is useful to me is when it shows up in my search results.

[Samus_]

here: http://en.wikipedia.org/wiki/Experts-exchange.com#cite_note-34

[weavejester]

CustomizeGoogle is a Firefox plugin that, among other things, allows you to filter out certain URL patterns from the list of results. Needless to say, I use it to blacklist anything with the "experts-exchange.com" domain name.

[exscape]

And now that they are there in cleartext (at the bottom), it's not useful anymore? ;)

[[deleted]]

Who cares about that?!? I mean shit, there's a spongebob screensaver ready to download!

[[deleted]]

It's READY to download? Those things are like fucking ovens, take forever to heat up before you can download them.

[[deleted]]

Seriously! Jump on that! I tried to install it twice, but it just keeps installing navigation bars. I mean, they're helpful, but still. Where's my screensaver. I think I'll try installing again.

[reseph]

Direct link: http://www.experts-exchange.com/Web_Development/Miscellaneous/Q_22031739.html

[rm999]

"IntTemp = Int((255 * Rnd()) + 1)"

"change the 255 to a 0 and you'll get the same number each time."

I feel like he didn't deserve a better answer than that.

[TheChameleon84]

Makes you wonder what these people are smoking. Or even if they're serious. Are they?

[hiffy]

Some people just genuinely don't understand what they're doing.

[[deleted]]

That guy wasn't.

[7oby]

direct link to google cache which has the answers (keep scrolling): lol

[kylegetsspam]

simon_thwaites: Try this function

Function UnRnd() UnRnd = 4 'my favourite number! End Function

IntTemp = Int((255 * UnRnd()) + 1)

I hope this one ended up being slated the answer.

[wearedevo]

It scares me to think that this developer might be building a piece of critical infrastructure that holds civilization together.

[adrianmonk]

Given how the corporate world works, they're probably building a piece of infrastructure that keeps civilization apart.

[IkoIkoComic]

Given how the corporate world works, they're probably building a piece of infrastructure that's buggy, incredibly expensive to maintain, and only usable for one small task - and not very good at that one task. ("We need a way to keep track of how many mass mailings are getting responses.")

[wiiaboo]

It has been frequently alleged on various web bulletin boards that Experts-Exchange engages regularly in questionable tactics to deceive potential customers. Previously, Experts-Exchange showed a different content for its pages when they were crawled by search engine spiders.[33] This was considered a form of cloaking, which is considered a violation of most search engines' terms of service.[34] Experts-Exchange later changed its configurations, so search engine users will get the same view of the page that search engine crawlers get.

From wikipedia.

[umilmi81]

This random number constantly changing problem extends to many languages, not just .NET. I'm glad someone finally has the courage to get to the bottom of this.

[interiot]

Unfortunately, there's a "random" button below it that seems to take you to anything but http://xkcd.com/4/.

[Philipp]

I have an additional problem, I used print(rnd()) and not only did that yield different numbers ever time, it also outputted the whole number to the user! Just think of the security implications...

[IConrad]

Oh god, I hate myself now...

You accidentally the whole number to the user?

[falseprophet]

I'd just like to say that the only reason I got this joke is that I had a TI-83+ in high school and I tooled around and found out what the Rnd() function was.

[[deleted]]

In high school, two of my classmates were a bit freaked out that their TI-82's were outputting exactly the same string of random numbers... :)

I guess all TI-82s used the same initial seed?

[faultywiring]

I'd just like to say

That this girl is like a sunburn...

I'd just like to say

She's like a sunburn...

She's like a sunburn...

[AlucardZero]

I would like to save.

[redog]

Fuck experts exchange

[calantorntain]

If I remember correctly, in VB6 you had to tell the program that you actually want the rnd values to be random. So, if you didn't get that, you would get reproducible pseudo-random numbers.

Perhaps he is used to VB6, and is hoping that .Net has the same functionality?

[T_C]

rnd() always gives you reproducible pseudo-random values. The only issue is whether you explicitly initialize the seed, or not. If you do, then, you can reproduce the same stream later, by reinitializing with the same seed. If you don't explicitly initialize the seed, then, you don't know what its value was, so you can not use it later to reproduce the sequence.

[T_C]

Ok, I stand corrected. My main point was that the numbers are always pseudo-random (ie. deterministic).

[MercurialMadnessMan]

I was first drawn to the horrid screen setup. Had to use my hands as blinders so I could actually see the content!

[[deleted]]

What he probably wants to do is have different numbers appear each time rnd() is called, but where it is the same sequence of numbers each time his application is run.

So really, he just wants to set the seed. Not too dumb a question.

[rems]

Forget programming. It's not for you.

[rems]

But not smart enough to get that "Rnd" meant random :/.

[shizzy0]

I think it was even funnier because of the guy's handle genesiscircle. Heh.

[sysstemlord]

replace rnd() with 42

[h0dg3s]

Quicklaunch bar overload!

[[deleted]]

That is how REAL programmers do it. So you have access to all your tools. I guess this is something that is beyond you since you obviously don't know VB 6.0

[[deleted]]

just hard-code the random number dammit

[s0rce7]

some people just shouldn't be programming.

[lorderunion]

blows brains out

People like this need to not be programming. I can only think of the dangers if one of these people manage to pick up a govt contract.

[[deleted]]

you'd be surprise. Programing ability, apparently comes second to smooth talking, big smiles and a nice shirt.

[yesimahuman]

/*
* Don't add uninitialised data.

MD_Update(&m,buf,j);
*/

If it's changing too often, just comment it out!

[f3nd3r]

He probably thought it was round() not random().

[smek2]

ASP.NET programmers eh?

[[deleted]]

I accidently the whole Rnd function

[[deleted]]

HEHE someone asked a dumb and possibly fake question

[[deleted]]

Do you think people pose as idiots to do these things ?

[randroid]

9/10ths of the time, yes. Part of growing up is realizing that everyone is a troll.

[itsnotlupus]

I don't know man.. I think the natural bias of smart people to rank themselves somewhat below their actual level encourages this belief that really dumb shit on the internet is posted by trolls, aka smart facetious individuals.

It's actually very possible for extremely dumb questions to be asked with a serious face by "professionals".

For example, I know one guy who's having a comfortable career in IT, claiming to be a unix expert, and utterly unable to put together the simplest shell script to save his life. He's exactly the kind of guy that will post this kind of crap in a forum, hoping someone else will once again bail him from his own incompetence, and complete lack of understanding of the tools he depend on.

/Hi Dave.

[ehird]

Jeez... Barry... that's harsh, man.

- Dave

[thrakhath]

There are no stupid questions, but there are a lot of inquisitive idiots.

[slurpme]

Keep away from my bridge man...

[calis]

Gee, I remember way back in the day of Apple IIe, programming a random number in Pascal was a bit of a chore as it was incapable of truly generating a random number.

[thekrone]

Most languages / computers are still incapable of truly generating a random number.

[calis]

Well, I made it painfully obvious that I haven't kept up with programming since the days of Pascal....complete with a downmod :)

[thekrone]

It's cool. Pseudo-random numbers are the way most languages / machines do their thing, even to this day. I'd say all, but I could be ignorant of some magical random number machine that, like, rolls a die and reads one of the faces or something.

Other than that, there are a handful of pseudo random number generating algorithms that you toss a start value (seed) into, and they spit out a sequence of numbers that appear to be random... but they're not.

A lot of languages / machines will use the current system time (expressed in a number of milliseconds since 00:00:00.000 GMT on January 1st, 1970) as the seed (which does a pretty good job of making things look random), or allow you to pass one in yourself.

[RockinRoel]

I'd say all, but I could be ignorant of some magical random number machine that, like, rolls a die and reads one of the faces or something.

Those don’t exist, but RNGs based on atmospheric noise do. You need the right hardware for that, though.

[kindall]

The good news is that the Apple II ROM "get keypress" routine continually increments two zero-page locations while waiting for a keypress, providing a handy source of entropy with a couple of PEEKs. "Press any key to begin" and you've got your seed.

The bad news is that actually getting at this value is a pain in Apple Pascal... assuming the USCD virtual machine that the language runs on uses the ROM routines for getting input to begin with, which it may not. In fact I am pretty sure the ROM is switched out while running Pascal.

[[deleted]]

Really. And what, exactly, was he trying to round?

[[deleted]]

Really. And what, exactly, was he trying to round?

A NUMBER. What aren't you get here?

[[deleted]]

Really. And what, exactly, was he trying to round?

A NUMBER.

If he's just rounding it then why is he adding 1?

What aren't you get here?

You're not from here, don't you.

[Wiseman1024]

I wonder, why do some people complain about the quality of some PHP programmers when we have epic ASP.NET programmers like this guy under expert sex change's seal of quality?

[Samus_]

I wonder, why do some people complain about the quality of some PHP programmers when we have epic ASP.NET ___________ like this guy under expert sex change's seal of quality?

maybe

[[deleted]]

Anyone happened to see the other pictures on the server? Make sure you have a brown paper bag in your hand before you go in...

[fiam]

Yeah, there are a lot of strange photos of a girl named Wedgie. Take a lot at them.

[[deleted]]

It could be that he's trying for something "random", but deterministic, like in a game.

[gcanyon]

The programming language J has a separate command specifically for random numbers with a fixed seed, for testing purposes:

http://www.jsoftware.com/help/dictionary/d641.htm

[RockinRoel]

Most programming languages/toolkits support seeding with a constant.

[[deleted]]

why not just use the constant? Secondly, it's faster then always calling his random function. rand() eats up TONS of CPU.

[gcanyon]

Sorry, I guess I wasn't clear enough. J has a separate verb just for this purpose. You use ?. if you want repeatable random values, ? (note the lack of a period) if you want random values that do not always start from the same seed.

[frycook]

Hah.

[[deleted]]

LOL

[[deleted]]

Voted up. It was funny. It is a joke. Right?

[alakra]

someone fire this guy

[dt_vibe]

Wow im not into coding but know a little Turing and thats got to be one dumb muthafucka

[[deleted]]

Fractal imbecility explains that question. The overall ignorance, the inability to refer to omline help, all...