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randInt( Problems
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Spenceboy98


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Joined: 06 Jan 2012
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Posted: 30 Jan 2012 05:00:02 pm    Post subject: randInt( Problems
Whenever I try to use the "randInt(" command on my TI-84+ SE it says, "ERR:OVERFLOW". It worked fine before. I don't know what is wrong. Help would be appreciated!
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Tari


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Posted: 30 Jan 2012 05:01:01 pm    Post subject:
When in doubt, try reseeding the RNG.

Code:
0->rand

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elfprince13


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Posted: 30 Jan 2012 05:03:57 pm    Post subject:
Can you give us an example of a line you are executing that is causing the problem?

Tari wrote:
When in doubt, try reseeding the RNG.

Code:
0->rand


Keep in mind that whenever you issue this command, your "random" numbers will follow the same sequence.
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Spenceboy98


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Posted: 30 Jan 2012 05:06:06 pm    Post subject:
Thanks! It works now!
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Sorunome


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Posted: 31 Jan 2012 05:26:55 am    Post subject:
Tari wrote:
When in doubt, try reseeding the RNG.

Code:
0->rand
What does that exactly do? Does it somehow say out of which number the "random" numbers are calculated?
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Ashbad


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Joined: 01 Dec 2010
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Posted: 31 Jan 2012 07:49:19 am    Post subject:
Sorunome wrote:
Tari wrote:
When in doubt, try reseeding the RNG.

Code:
0->rand
What does that exactly do? Does it somehow say out of which number the "random" numbers are calculated?


Simpler random number generators work by starting with a certain number, and then each time you want a new random number, it'll do something like multiply the number by some arbitrary number (like .123456789 or .54321876) and then add another arbitrary number to it (again, like .12345), and will then consider that "random". When you re-seed the generator, you get the same sequence of results every time you use rand because it starts with the same number as the seed, and multiplies/adds the random numbers on top the same each time. The trick is to start with something rather naturally random as the seed, like a Timer ID/ Timer Status, and then don't reseed it more often than you need to (if at all).
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Travis


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Joined: 03 Feb 2011
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Location: Kansas, USA
Posted: 31 Jan 2012 08:02:20 am    Post subject:
It's also useful for experiments or debugging where you want to be able to reuse the same PRNG sequence on multiple trials—just use the same seed again.

I remember the “overflow” problem being mentioned frequently back in the TI-82/85 ASM days after people would run certain programs. I guess the seed value in RAM would get corrupted and cause the error until the seed was manually reset to a valid value.
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KermMartian


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Posted: 31 Jan 2012 08:10:23 am    Post subject:
Travis wrote:
I remember the “overflow” problem being mentioned frequently back in the TI-82/85 ASM days after people would run certain programs. I guess the seed value in RAM would get corrupted and cause the error until the seed was manually reset to a valid value.
Exactly this. I've never quite understood why the OS doesn't choose to reset the rand seed to a sane value if it's a non-number; either TI's engineers didn't think to catch and handle that error, or they decided it would be the least confusing behavior since you might not suddenly expect your rand to be reseeded.
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Weregoose


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Joined: 23 Oct 2009
Posts: 463
Posted: 31 Jan 2012 07:40:46 pm    Post subject:
To mimic seeding rand:

PROGRAM:RANDSEED
:abs(int(Ans→X
:2^31-{85,249→u(nMin)
:4E4+{14,692→v(nMin)
:{XAns(1),X
:15{823,4526}not(X)+Ans-u(nMin)int(Ans/u(nMin)→w(nMin)

To mimic rand:

PROGRAM:RAND
:v(nMin)w(nMin)
:Ans-u(nMin)int(Ans/u(nMin)→w(nMin)
:fPart(1-min(ΔList(Ans/u(nMin)

This is good up to and including X=109-1. Why the native variety takes a different course is anyone's guess.
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