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Do you have an idea to simulate a coin flip?

Now I have

return 'Heads' if Math.random() < 0.5

Is there a better way to do this?

thanks

edit: please ignore the return value, and "better" means an exact probability of 50-50.

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9 replies


always dead simple

coin = rand (1);



in many scripting languages ​​this will give you a random int between 0 and your argument, so passing 1 gives you 0 or 1 (head or tail).

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Numerical recipes in C say they don't trust built-in random number generators when it matters. You could probably implement the algorithm shown in the book as a function ran1 (), which it claims passes all known statistical randomness tests (in 1992) for less than about 10 8 calls.

The basic idea of ​​the ran1 () algorithm is to add an arbitrary move to the output of the random number generator to reduce the sequential low order correlations. They use Shays from Bays-Durham from section 3.2-3.3 in Art of Computer Programming Volume 2, but I would suggest that you can use Fisher-Yates shuffle too.



If you need more random values, then the same document also provides a generator (run2), which should be useful for values ​​at least 10 17 (my guess is based on a period of 2.3 x 10 18 ). There is also a function (ran3) that uses a different method to generate random numbers in case linear congruential generators give you some kind of problem.

You can use any of these functions with your <0.5 to make sure you get an even distribution.

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the statement xkcd is true:

string getHeadsOrTails {
        return "heads"; //chosen by fair coin toss,
                        //guaranteed to be random
    }
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What you have is how I will do it. If 0.0 <= Math.random () <1.0, as standard, then (Math.random () <0.5) is going to give you heads when Math.random () is between 0.0 and 0.4999 ... and tails when it's between 0.5 and 0.999 ... This is as honest a coin flip as you can get.

Of course, I assume a good implementation of Math.random ().

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On a Linux system, you can read a bit from / dev / random to get the "best" random data, but an almost random method like Math.Random () is fine for almost any application you can think of except for serious cryptographic works.

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Try to differentiate between odd and even numbers. Also, return an enum value (or boolean), not a string.

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I cannot comment on people's posts because I have no reputation, but only FYI about the whole <= vs. <topic covered in the Bill. Lizard's comment: Since it can be assumed that random generates any number between 0-1 (which is technically not the case due to the size limitation of the floating point number, but more or less true in practice) there will be no difference in num <= .5 or num <.5 because the probability of getting any one number in any continuous range is 0. IE: P (X = .5) = 0 when X = a random variable between 0 and 1.

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The only real answer to this question is that you cannot "guarantee" the likelihood. If you think about it, a real coin acceptor does not guarantee a 50/50 probability, it depends on the coin, the person flipping it, and if the coin is dropped and rolled across the floor.;)

The point is that it is "quite random". If you are simulating a coin flip, then the code you posted is more than good.

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Try

return 'Heads' if Math.random() * 100 mod 2 = 0

I don't really know what language you are using, but if a random number is divisible by two, then these are chapters, if they are not, they are tails.

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