Hal Ashburner-2 wrote:
>
> chase321 wrote:
>> I have been using Gnumeric for some time in the statistics classes I
>> teach.
>> This past semester, I did my first online section, and had them submit
>> labs
>> using Gnumeric. For one lab, I had them use the "randbetween" function
>> to
>> generate random numbers. 9 of the 17 labs I received had identical sets
>> of
>> random numbers. This makes me more than a little suspicious, but I have
>> also seen students get the same sequence of numbers in the classroom. I
>> know enough about pseudorandom number generators to know that if two
>> people
>> start at the same point in the sequence, they're going to get the same
>> set
>> of numbers. So I have two questions.
>> 1) How is the pseudorandom number generator initialized (seeded)?
>> 2) Is there any way to seed it manually? I can find no function for this
>> mentioned in the manual.
>>
>> Thanks for any help.
>
> Hi Chase,
> Looking at the code in plugins/fn-random/functions.c and src/mathfunc.c
> it appears rand_01 is the relevant function. By setting the environment
> variable GNUMERIC_PRNG_SEED
> (on unix with a bourne compatible shell with something like
> $ export GNUMERIC_PRNG_SEED=some_random_string
> ) will cause rand_01 to use a pseudo random number generator using the
> specified seed. Otherwise it should get its random numbers from
> /dev/urandom
>
> My understanding of this is that if GNUMERIC_PRNG_SEED is set then each
> time you open a sheet containing randbetween you will get the same
> value, whereas if it isn't then you won't.
>
> Are you using windows by any chance?
>
> Kind regards,
> Hal
>
>
> I'm using Linux, but most if not all of my students are using Windows.
> What I actually had them do is generate the random numbers and then copy
> and paste "as value" so the numbers would stay fixed for the rest of the
> activity. So I should be getting the actual numbers that they got. Of
> course, if one of them did the lab and then passed the finished product
> around to the others, that would certainly explain it, but I don't want to
> claim that if I'm not sure.
> Would the Windows installer set the environmental variable? I can check
> tomorrow to see if it's set on my Windows machine at the office.
> Incidentally, grades are already in, so I won't be taking this to the dean
> at this point, but I would like to know what's going on.
> Thanks for the quick reply!
> --Chase
> _______________________________________________
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>
>
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