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Re: strange random behavior ?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg69948] Re: strange random behavior ?
*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
*Date*: Thu, 28 Sep 2006 06:15:00 -0400 (EDT)
*Organization*: The Open University, Milton Keynes, UK
*References*: <efdjca$je$1@smc.vnet.net>
Arkadiusz.Majka at gmail.com wrote:
> Hi,
>
> For
>
> SeedRandom[7]
> Table[Random[Integer, {1, 6}], {5}]
> Table[Random[Integer, {1, 3}], {5}]
>
> I get
>
> Out[32]=
> {2,1,6,2,6}
>
> Out[33]=
> {2,1,3,1,3}
>
> When i repeat I obviosly get the same (magic of seedrandom)
>
> SeedRandom[7]
> Table[Random[Integer, {1, 6}], {5}]
> Table[Random[Integer, {1, 3}], {5}]
>
>
> Out[32]=
> {2,1,6,2,6}
>
> Out[33]=
> {2,1,3,1,3}
>
> Bu when I change the range of random numbers in generation of the first
> list , say 1->2
>
> SeedRandom[7]
> Table[Random[Integer, {2, 6}], {5}]
> Table[Random[Integer, {1, 3}], {5}]
>
> I get
>
> Out[35]=
> {3,2,3,6,6}
>
> Out[36]=
> {2,2,3,1,3}
>
> Since Seed is still the same (7), why second list is changed? (Out[36]
> does not equal to Out[33])
SeedRandom[] guarantees that the *initial* value -- the starting point
-- used to generate a sequence of the pseudo-random number is the same
every time the function SeedRandom is executed during a computation or
after the kernel has been restarted.
Now, to get the same sequence of pseudo-random numbers, one must use the
*same* series of calls to functions like Random; that is same order,
same parameters.
> This behavior does not take place when we do not deal with tables but
> with single elements.
Here, I am not sure what you are talking about, but using Table or not
does not change the values generated:
In[1]:=
SeedRandom[7]
Random[Integer, {2, 6}]
Random[Integer, {2, 6}]
Random[Integer, {2, 6}]
Random[Integer, {2, 6}]
Random[Integer, {2, 6}]
Random[Integer, {1, 3}]
Random[Integer, {1, 3}]
Random[Integer, {1, 3}]
Random[Integer, {1, 3}]
Random[Integer, {1, 3}]
Out[2]=
3
Out[3]=
2
Out[4]=
3
Out[5]=
6
Out[6]=
6
Out[7]=
2
Out[8]=
2
Out[9]=
3
Out[10]=
1
Out[11]=
3
In[12]:=
SeedRandom[7]
Table[Random[Integer, {2, 6}], {5}]
Table[Random[Integer, {1, 3}], {5}]
Out[13]=
{3, 2, 3, 6, 6}
Out[14]=
{2, 2, 3, 1, 3}
Regards,
Jean-Marc
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