[PD] help_random/seed

cem guney cemthemuteguney at yahoo.com
Sun Jul 5 11:11:04 CEST 2009


hi, 

thanks much for your response!

also in regards to your explanation,

"It would be nice if the random source could be independently specified for all the pd objects that use random numbers, 
since the count of unreachable combinations when using the standard deterministic chaos generators is infinite"

any application examples as to why it would be nice if the random source could be independently specified?

cheers, :) 

 
Cem Güney
 
myspace. . lastfm. . tumblr. . cronica 




________________________________
From: Martin Peach <martin.peach at sympatico.ca>
To: Mike Moser-Booth <mmoserbooth at gmail.com>
Cc: pd-list at iem.at; IOhannes m zmölnig <zmoelnig at iem.at>
Sent: Sunday, July 5, 2009 7:22:51 AM
Subject: Re: [PD] help_random/seed

Mike Moser-Booth wrote:
> IOhannes m zmölnig wrote:
>> Frank Barknecht wrote:
>>> Hallo,
>>> cem guney hat gesagt: // cem guney wrote:
>>> 
>>>> just started studying PD. going through the control examples i've been stuck trying to figure out the function of the message, seed 123 in the
>>>> example for "random". not sure if i figured out the explanation below,
>>>> 
>>>> Seeds are kept locally so that if two Randoms are seeded the same they will have the same output (or indeed you can seed the same one twice to repeat the output.)
>>> 
>>> Yes, that's true, you understood correctly.
>>> 
>>> Oh, wait, that's what's in the help-file! What exactly is cloudy there?
>> 
>> probably the simple fact, that [random] despite of it's name does not really produce random numbers.
>> mostly when computers present you a "random" number, then this number will only appear to be random, but in reality is just calculated as the next item of a totally deterministic series.
>> (as a matter of fact, a new random number is usually generated by simple taking the last number and then applying some more or less complicated transformation on this number). this method is known as "pseudo random".
>> 
>> you can set the "starting point" of the series by setting the "seed", which is the first number of the random sequence). since all [random] object use the same algorithm to calculate the next pseudo-random number, they will all end up with the same sequence if they all start with the same "seed".
>> by default Pd uses different seeds for all [random] objects so they all appear to work independently.
> In addition, it's probably worth mentioning that Pd will produce the same seeds for each [random] every time you load the patch. So while they appear to work independently, you will still get the same results each time you first run a patch after loading it.
> 

A lot of the latest cpus have hardware random number generators that work by having a jittery oscillator sample the cpu clock, or something along those lines. (Such a jittery oscillator is assumed to have normally distributed transition times.)
It would be nice if the random source could be independently specified for all the pd objects that use random numbers, since the count of unreachable combinations when using the standard deterministic chaos generators is infinite.

Martin


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