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<pre style="word-wrap:break-word; font-size:10.0pt; font-family:Tahoma; color:black">Thank you all.
By using X*1000, Y*1000 and the sum *1000 I got sufficiently random numbers.
Bengt
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----- Ursprungligt meddelande -----
Från: Tony Rogvall <tony@rogvall.se>
Till: Bengt Kleberg <bengt.kleberg@ericsson.com>
Kopia: "erlang-questions@erlang.org" <erlang-questions@erlang.org>
Skickat: 27-10-2013 6:14 em
Ämne: Re: [erlang-questions] more random uniform
</pre>
<div>No it was not necessary, just making sure it was fresh every time.
<div><br>
</div>
<div>Any particular reason to keep the third argument to zero in the random:seed/3 call ?</div>
<div>This will, as you point out, generate an initial sequence of small random:uniform numbers.</div>
<div>Looking at random.erl the calculation is (modified in this context):</div>
<div><br>
</div>
<div><span class="Apple-tab-span" style="white-space:pre"></span>(((X+1)*171) rem 30269) / 30269 +</div>
<div><span class="Apple-tab-span" style="white-space:pre"></span>(((Y+1)*172) rem 30307) / 30307 + </div>
<div><span class="Apple-tab-span" style="white-space:pre"></span>(((0+1)*170) rem 30323) / 30323</div>
<div><br>
</div>
<div>Keeping the X and Y small enough (less than 176 ) we can rewrite this as:</div>
<div><br>
</div>
<div><span class="Apple-tab-span" style="white-space:pre"></span>R = ((X+1)*171) / 30269 + ((Y+1)*172) / 30307 + 170 / 30323</div>
<div><br>
</div>
<div>The value of this expression will be small given small values on X and Y, and the expression</div>
<div>trunc(R*3) will be zero for X+Y < 56 (roughly)</div>
<div><br>
</div>
<div>In other words use larger numbers, and use them all, when seeding the random number generator.</div>
<div><br>
</div>
<div>/Tony</div>
<div><br>
</div>
<div>
<div><br>
<div>
<div>On 27 okt 2013, at 11:48, Bengt Kleberg <<a href="mailto:bengt.kleberg@ericsson.com">bengt.kleberg@ericsson.com</a>> wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">
<div style="word-wrap:break-word">
<pre style="word-wrap:break-word; font-size:10pt; font-family:Tahoma">7> [erlang:spawn( fun() -> random:seed(X,Y,0), io:fwrite("~p ", [random:uniform(3)]) end ) || X<-lists:seq(1,10), Y<-lists:seq(1,10)].
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
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Skickat: 27-10-2013 11:33 fm
Ämne: Re: [erlang-questions] more random uniform
</pre>
<div>
<pre style="word-wrap:break-word; font-size:10pt; font-family:Tahoma">Thank you.
I have 15B.
Is the erase/1 necessary? I am using new processes each time.
Bengt
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Till: Bengt Kleberg <<a href="mailto:bengt.kleberg@ericsson.com">bengt.kleberg@ericsson.com</a>>
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Skickat: 27-10-2013 11:13 fm
Ämne: Re: [erlang-questions] more random uniform
</pre>
<div>I can not replicate this (on R16B01).
<div><br>
</div>
<div>
<div>> erase(random_seed), random:seed(erlang:now()), random:uniform(3).</div>
<div>1</div>
<div>
<div>> erase(random_seed), random:seed(erlang:now()), random:uniform(3).</div>
<div>2</div>
</div>
<div>...</div>
<div><br>
</div>
<div>?</div>
<div><br>
</div>
<div>/Tony</div>
<div><br>
</div>
<div><br>
<div>
<div>
<div>On 27 okt 2013, at 10:45, Bengt Kleberg <<a href="mailto:bengt.kleberg@ericsson.com">bengt.kleberg@ericsson.com</a>> wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">Greetings,<br>
<br>
When doing random:uniform/1 for small values, ie 3, the result is 1 the first time. Changing the seed does not help.<br>
What am I missing?<br>
<br>
<br>
Bengt<br>
<br>
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gradually write over each other's libraries, partial upgrades occur, user and system errors happen, and minute changes may be unnoticeable and difficult to fix"</span></div>
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