[Coco] Is the RND command really generating a random number?

[Arthur Flexser]

The Wikipedia article cited earlier in this thread has a section on the
period length of the sequence:

https://en.wikipedia.org/wiki/Linear_congruential_generator

Art

On Fri, May 19, 2017 at 12:20 PM, John Guin <johnguin at hotmail.com> wrote:

> Did anyone ever try to figure out how "long" the list of numbers was
> before it started repeating?
>
> There is probably an analytic way of doing this based on the algorithm
> being used, but I can't help but wonder if rounding errors might skew the
> results.
>
> John
>
> -----Original Message-----
> From: Coco [mailto:coco-bounces at maltedmedia.com] On Behalf Of Arthur
> Flexser
> Sent: Friday, May 19, 2017 9:13 AM
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> Subject: Re: [Coco] Is the RND command really generating a random number?
>
> RND(TIMER) will just give a random number between 0 and whatever the
> current value of TIMER is.  RND with a negative argument will reseed the
> random number generator, starting the upcoming sequence of random numbers
> in a different place than where it would ordinarily start.  RND(-TIMER)
> makes the seed dependent on the TIMER value, so you'd get a different
> sequence of pseudo-random numbers each time you run the program.
> RND(TIMER) will only affect the scaling of the current random number to
> make it within the required interval, but won't affect the underlying
> sequence of numbers generated.
>
> Art
>
> On Fri, May 19, 2017 at 11:10 AM, Salvador Garcia via Coco <
> coco at maltedmedia.com> wrote:
>
> > Why won't RND(TIMER) work?
> >
> > Thanks, Salvador
> >
> >       From: Arthur Flexser <flexser at fiu.edu>
> >  To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> >  Sent: Thursday, May 18, 2017 11:26 PM
> >  Subject: Re: [Coco] Is the RND command really generating a random
> number?
> >
> > RND(TIMER) will not work for seeding the random number generator.  It
> > has to be RND(-TIMER) with a minus sign.
> >
> > Art
> >
> > On Thu, May 18, 2017 at 10:52 PM, Bruce W. Calkins <
> > brucewcalkins at charter.net> wrote:
> >
> > > Short answer: No.
> > >
> > > Longer answer: RND calls some sort of psudo-random lookup table. If
> > > you enter the table at the same point you will get the same sequence
> out.
> > You
> > > need to "randomize" the entry point.  As someone mentioned one
> > > method is
> > to
> > > add the command RND(timer) Which calls the current timer value,
> > > which is generally different each time, one is hard pressed to turn
> > > on their CoCo, load a program and run it in the same time repeatedly.
> > >
> > > Bruce W.
> > >
> > >
> > >
> > >
> > > On 05/18/2017 08:39 PM, Rietveld Rietveld wrote:
> > >
> > >> I used the RND command to generate a random game play option in the
> > >> cocoflash, but it doesn't seem to be very random. Some titles come
> > >> up
> > more
> > >> than the laws of probability would suggest is possible.  instead I
> > >> am
> > now
> > >> using a small math equation that uses a PEEK of the clock value.
> > >> This
> > has
> > >> resulted in a far more random looking selection
> > >>
> > >> Sent from my BlackBerry 10 smartphone.
> > >>
> > >>
> > >
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> > >
> >
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