Thread Subject:

MATLAB produces the same random number after being restarted

Hello,

I have a question on random number generator in MATLAB.
If I generate 10 random numbers like randi(10,[1 10]), and immediately after that I restart MATLAB and do the same thing, I will get exactly the same set of numbers.
So I want to ask if there is a way to break this issue.

This issue rises when I run a simulation with MATLAB in the command mode.
I want to run the same program for several times to get the statistics but it keeps producing exactly the same data everytime.

Is there a command that will break the computer clock or something that can make MATLAB to start with a new random number?

Thanks,
Tung

"Tung Le" <dexturelab@yahoo.com> wrote in message <jrqqjt$bu0$1@newscl01ah.mathworks.com>...
>
> Is there a command that will break the computer clock or something that can make MATLAB to start with a new random number?
===============

Yes. The RNG command.

"Matt J" wrote in message <jrqs4k$i62$1@newscl01ah.mathworks.com>...
> "Tung Le" <dexturelab@yahoo.com> wrote in message <jrqqjt$bu0$1@newscl01ah.mathworks.com>...
> >
> > Is there a command that will break the computer clock or something that can make MATLAB to start with a new random number?
> ===============
>
> Yes. The RNG command.

Could you make it a little bit more clear?
When I typed RNG into cmd, it couldn't recognize this command.

For example,
In cmd, I typed:
    matlab -r "randi(10, [1 10])"
then
    rng ===> not working!

Thank you.
Tung

"Tung Le" <dexturelab@yahoo.com> wrote in message <jrqtc0$n1a$1@newscl01ah.mathworks.com>...
>
> Could you make it a little bit more clear?
> When I typed RNG into cmd, it couldn't recognize this command.
>
> For example,
> In cmd, I typed:
> matlab -r "randi(10, [1 10])"
> then
> rng ===> not working!
====================

RNG is a MATLAB command, not a cmd command. Run "doc rng" within a MATLAB session to learn its usage. I think you probably want the syntax

rng('shuffle');

I don't recommend trying to control the conditions in which MATLAB starts up from outside MATLAB. You should use a startup.m file (see "docsearch startup").

I would also think carefully whether you want the random number generator to run differently every time MATLAB starts up. It will make your work hard to reproduce. You can always issue RNG commands inside particular code routines in the particular cases when you're certain you want non-reproducible behavior.

 

"Matt J" wrote in message <jrqvl4$2kj$1@newscl01ah.mathworks.com>...
> "Tung Le" <dexturelab@yahoo.com> wrote in message <jrqtc0$n1a$1@newscl01ah.mathworks.com>...
> >
> > Could you make it a little bit more clear?
> > When I typed RNG into cmd, it couldn't recognize this command.
> >
> > For example,
> > In cmd, I typed:
> > matlab -r "randi(10, [1 10])"
> > then
> > rng ===> not working!
> ====================
>
> RNG is a MATLAB command, not a cmd command. Run "doc rng" within a MATLAB session to learn its usage. I think you probably want the syntax
>
> rng('shuffle');
>
> I don't recommend trying to control the conditions in which MATLAB starts up from outside MATLAB. You should use a startup.m file (see "docsearch startup").
>
> I would also think carefully whether you want the random number generator to run differently every time MATLAB starts up. It will make your work hard to reproduce. You can always issue RNG commands inside particular code routines in the particular cases when you're certain you want non-reproducible behavior.
>
>

It's working now.
Thank you.

"Tung Le" <dexturelab@yahoo.com> wrote in message <jrqtc0$n1a$1@newscl01ah.mathworks.com>...
> "Matt J" wrote in message <jrqs4k$i62$1@newscl01ah.mathworks.com>...
> > "Tung Le" <dexturelab@yahoo.com> wrote in message <jrqqjt$bu0$1@newscl01ah.mathworks.com>...
> > >
> > > Is there a command that will break the computer clock or something that can make MATLAB to start with a new random number?
> > ===============
> >
> > Yes. The RNG command.
>
> Could you make it a little bit more clear?
> When I typed RNG into cmd, it couldn't recognize this command.

Whenever you want information about a name or command, use the commands
help, doc and type. For example,

help rng
doc rng
type rng

Hope this helps.

Greg

"Tung Le" <dexturelab@yahoo.com> wrote in message
news:jrqqjt$bu0$1@newscl01ah.mathworks.com...
> Hello,
>
> I have a question on random number generator in MATLAB.
> If I generate 10 random numbers like randi(10,[1 10]), and immediately
> after that I restart MATLAB and do the same thing, I will get exactly the
> same set of numbers.

That's correct.

http://www.mathworks.com/help/techdoc/math/bs1qb_i.html

Read through the "Starting Over" portion of that page.

> So I want to ask if there is a way to break this issue.
>
> This issue rises when I run a simulation with MATLAB in the command mode.
> I want to run the same program for several times to get the statistics but
> it keeps producing exactly the same data everytime.
>
> Is there a command that will break the computer clock or something that
> can make MATLAB to start with a new random number?

As others have said, have your function call RNG (once; don't call it
repeatedly in a loop hoping to make the numbers "more random" or anything
like that -- that tends to make the numbers "less random" in some sense, if
I recall correctly.)

--
Steve Lord
slord@mathworks.com
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