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]

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]

"geoffp" <fw*****@jhgjhfggb.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, ti**@probo.com
Providenza & Boekelheide, Inc.

[geoffp]

"Tim Roberts" <ti**@probo.comwrote in message
news:v8********************************@4ax.com...

"geoffp" <fw*****@jhgjhfggb.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, ti**@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]

"Tim Roberts" <ti**@probo.comwrote in message
news:v8********************************@4ax.com...

"geoffp" <fw*****@jhgjhfggb.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, ti**@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.