Changing the matlab seed

The seed is not changing when I close the Matlab and open a new one. The seed is always being set as 0. How can I fix this?

[KALYAN ACHARJYA]

Detail, please?

Answer 1

[Bjorn Gustavsson]

Your question is a bit on the vague end - but I'll guess that you're asking about the seed for the random number generator...

If that's the case you should take a look at the help for rand, or look for the documentation pages "Updating Your Random Number Generator Syntax". From the former there is a link towards the latter, the latter describes in detail how to randomize the start of the random number sequence...

HTH

[Arvind Ganesh]

Yes, my question was about random number generator only. The issue is not the syntax.

Say I open two or three new Matlab windows, and execute the command:

rand(2,2)

Then, all 3 windows produce the same output (the output with seed 0 set by command rng(0)). Why is this so? This is not supposed to happen. The seed should change when I close and open a new Matlab window.

[Bjorn Gustavsson]

Well that this should or should not happen is a question about design choices and such. I've heard arguments for starting at the same point in the random number stream every time along the line of "if someone wants to test different algorithms with a pseudo-random data-set one should always compare the algorithms with identical data". You can of course put something like rng('shuffle') in your startup.m.

Then you only have to remember that when/if you need to run and rerun multiple algorithms with identical input you'll need to start the random number generator with the same seed.

HTH

[Stephen23]

"This is not supposed to happen. The seed should change when I close and open a new Matlab window."

Yes, it is supposed to happen. This is exactly the documented behavior. In fact this is such a common topic that there is a whole page devoted to explaining this:

https://www.mathworks.com/help/matlab/math/why-do-random-numbers-repeat-after-startup.html

That page also explains how to get different random numbers, and is easy to find using any internet search engine.

[Arvind Ganesh]

Thank you. That is helpful.

Answer 2

[Dennis]

You can use

   rng('shuffle')

For more information have a look here