reproducible random number series

[geoffp]

I need to generate reproducible random number series.

I've done the obvious - use mt_srand with the same seed. This supposedly
will create the same series every time.

Is this true? Its not working for me.

By the way, seeding mt_srand with different integers doesn't necessarily
produce different series. I've done a little testing and every pair of
consecutive even and odd numbers produces the same series. eg. seed 0 and 1
produce the same series, as does 10000 and 10001.

geoffair in xgmailx xcomx

[davie]

Re: reproducible random number series


geoffp wrote:

I need to generate reproducible random number series.
>
I've done the obvious - use mt_srand with the same seed. This supposedly
will create the same series every time.
>
Is this true? Its not working for me.
>
By the way, seeding mt_srand with different integers doesn't necessarily
produce different series. I've done a little testing and every pair of
consecutive even and odd numbers produces the same series. eg. seed 0 and 1
produce the same series, as does 10000 and 10001.
>
geoffair in xgmailx xcomx

As of PHP 4.2.0, there is no need to seed the random number generator
with srand() or mt_srand() as this is now done automatically.

I assume you want the same series of random numbers ?
If this is the case generate your series and save to a file

[Tim Roberts]

Re: reproducible random number series

"geoffp" <fwerfrf@jhgjhf ggb.comwrote:

>I need to generate reproducible random number series.
>
>I've done the obvious - use mt_srand with the same seed. This supposedly
>will create the same series every time.
>
>Is this true? Its not working for me.

Really? I did this:

<?php
mt_srand(1000);
echo mt_rand(), "\n";
echo mt_rand(), "\n";
echo mt_rand(), "\n";
echo mt_rand(), "\n";
?>

and it produces the same sequence every time. Note that you can't rely on
the sequence continuing across pages.

>By the way, seeding mt_srand with different integers doesn't necessarily
>produce different series. I've done a little testing and every pair of
>consecutive even and odd numbers produces the same series. eg. seed 0 and 1
>produce the same series, as does 10000 and 10001.

You are correct. The code for mt_srand always sets the bottom bit.
--
- Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.

[geoffp]

Re: reproducible random number series


"Tim Roberts" <timr@probo.com wrote in message
news:v8gpf211m5 37rbitnonp10j93 5vetoenfd@4ax.c om...

"geoffp" <fwerfrf@jhgjhf ggb.comwrote:
>

>>I need to generate reproducible random number series.
>>
>>I've done the obvious - use mt_srand with the same seed. This supposedly
>>will create the same series every time.
>>
>>Is this true? Its not working for me.

>
Really? I did this:
>
<?php
mt_srand(1000);
echo mt_rand(), "\n";
echo mt_rand(), "\n";
echo mt_rand(), "\n";
echo mt_rand(), "\n";
?>
>
and it produces the same sequence every time. Note that you can't rely on
the sequence continuing across pages.
>

>>By the way, seeding mt_srand with different integers doesn't necessarily
>>produce different series. I've done a little testing and every pair of
>>consecutive even and odd numbers produces the same series. eg. seed 0 and
>>1
>>produce the same series, as does 10000 and 10001.

>
You are correct. The code for mt_srand always sets the bottom bit.
--
- Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.

Thanks Tim - I think I see whats happening.

I assumed that once srand had been seeded, the series would continue for
the whole session(I set it in the first page). From what you say I gather
that the series ends whenever you call a page, even though its got the same
PHP code. Then the randomiser is seeded automatically the first time its
called - DOH!

Geoff

[geoffp]

Re: reproducible random number series


"Tim Roberts" <timr@probo.com wrote in message
news:v8gpf211m5 37rbitnonp10j93 5vetoenfd@4ax.c om...

"geoffp" <fwerfrf@jhgjhf ggb.comwrote:
>

....

>
and it produces the same sequence every time. Note that you can't rely on
the sequence continuing across pages.
>

>>By the way, seeding mt_srand with different integers doesn't necessarily
>>produce different series. I've done a little testing and every pair of
>>consecutive even and odd numbers produces the same series. eg. seed 0 and
>>1
>>produce the same series, as does 10000 and 10001.

>
You are correct. The code for mt_srand always sets the bottom bit.
--
- Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.

Thanks Tim - I think I see whats happening.

I naively assumed that once srand had been seeded, the series would
continue for the whole session(I set it in the first page). From what you
say I gather
that the series ends whenever you call a page, even though its got the same
PHP code. Then the randomiser is seeded automatically the first time its
called - DOH!

Geoff

PS Some of my posts to this group don't seem to be appearing, so apologies
if you've got this twice. I don't often use newsgroups.