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Best of John Robison

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Ask the Slot Expert: Concerns about pseudo-random number generators

4 July 2012

Slot machines really have pseudo-random number generators (pRNG). A pRNG generates a number stream that appears to be random and satisfies many properties of randomness, but is actually generated by a deterministic function and is not truly random. Ron was right. Strictly speaking, the results on a slot machine are not truly random.

Dear John,

About your recent answer above to Wanda... John, surely you realized when you wrote that you would receive an avalanche of e-mails from your slot-playing readers begging, pleading, cajoling, insisting, demanding, and possibly even a few from the crazier ones threatening you if you did not further explain, expound, write a tome -- well, you get the picture, around the above statement. I for one am the "asking politely" type. I would specifically like you to expound on the two sentences that stick out (scream) in my mind, and that would be the two that read: "A pRNG generates a number stream that appears to be random and satisfies many properties of randomness, but is actually generated by a deterministic function and is not truly random... Strictly speaking, the results on a slot machine are not truly random."

It was lovely how you explained to Wanda about the pRNG and the RNG. I thought it was kind of you to give the nod to Ron. Your answer was informational. Thing is though, it's the information I quoted above that makes me lose that warm fuzzy feeling I was just beginning to re-experience. This bit about "a pRNG generates a number stream that appears to be random and satisfies many properties of randomness, but is actually generated by a deterministic function and is not truly random... Strictly speaking, the results on a slot machine are not truly random."

Well, quite frankly, John, that bit right there just about makes my blood run cold. It might not, if I knew exactly what in the world those words really mean in direct relationship to my feeding the one-armed bandit, especially online. For reasons of pure ignorance, I am now filled with superstitious daymares about that answer of yours. I wonder about the words ... "A pRNG generates a number stream that appears to be random and satisfies many properties of randomness..."

What I wonder is this: Who thinks it is OK that the number stream "APPEARS" to satisfy "MANY" properties of randomness? It doesn't satisfy me very much at the moment, so I am wondering about who might be satisfied by those cold words, except the people who are collecting my change from the machines, both online and off. Then there is that other terrifying string of words "...but is actually generated by a deterministic function and is not truly random... Strictly speaking, the results on a slot machine are not truly random."

John, I am asking you to please clarify this information for this now temporarily demented woman who understands very little of random number concepts and really cannot understand how something can be determined to be random, declared to be random, when it is in fact not random at all? How can they legally carry off such a thing? Please answer me, John, to quote the country/western song man..." I will be lying on my back, with tears in my ears from crying over you"...well your words any way! Until you do...

Thank you for your attention in this matter,
Irishgilly

Dear Irishgilly,

Calm down. Whether something is an RNG or a pRNG is only a matter of nomenclature. Both devices generate a stream of numbers that satisfy many of the tests for randomness. You would not be able to reliably distinguish a stream of numbers generated by a pRNG from that generated by an RNG.

I want to correct one statement you made. The stream of numbers from a pRNG does not "appear to satisfy many properties of randomness", it does satisfy many of those properties. You can search online to find many tests for randomness.

The pRNG in a slot machine is based on a mathematical formula. There can be no randomness in mathematical functions. Two plus two must always equal four. It can't sometimes equal four and sometimes equal three or five.

As long as a machine operates properly, each symbol is equally likely to land on the payline on every spin, there are no discernible patterns in its results, the results of each spin are unpredictable, and each player has an equal chance of winning on each and every spin, does it matter if the results are determined by numbers from an RNG or a pRNG?

Jackpots for all,
John


Send your slot and video poker questions to John Robison, Slot Expert, at slotexpert@comcast.net. Because of the volume of mail I receive, I regret that I can't reply to every question.

John Robison

John Robison is an expert on slot machines and how to play them. John is a slot and video poker columnist and has written for many of gaming’s leading publications. He holds a master's degree in computer science from the prestigious Stevens Institute of Technology.

You may hear John give his slot and video poker tips live on The Good Times Show, hosted by Rudi Schiffer and Mike Schiffer, which is broadcast from Memphis on KXIQ 1180AM Friday afternoon from from 2PM to 5PM Central Time. John is on the show from 4:30 to 5. You can listen to archives of the show on the web anytime.

Books by John Robison:

The Slot Expert's Guide to Playing Slots
John Robison
John Robison is an expert on slot machines and how to play them. John is a slot and video poker columnist and has written for many of gaming’s leading publications. He holds a master's degree in computer science from the prestigious Stevens Institute of Technology.

You may hear John give his slot and video poker tips live on The Good Times Show, hosted by Rudi Schiffer and Mike Schiffer, which is broadcast from Memphis on KXIQ 1180AM Friday afternoon from from 2PM to 5PM Central Time. John is on the show from 4:30 to 5. You can listen to archives of the show on the web anytime.

Books by John Robison:

The Slot Expert's Guide to Playing Slots