How to generate a random distribution.

Hi I'm doing a simple project for a course I'm in and I've been having trouble with some of the scripts my prof gives us. I think its because they're written for an older version of Matlab. I'm using matlab 2014a.

I think this code is supposed to generate a random distribution for x, but when I run it x ends up getting a stuck value, I know that's not supposed to happen. Can some one help?

function x=creature_state()
    x=floor(2.1*rand)+1;
return

[David Young]

I'm not sure what you mean by a stuck value. The function returns the value 1, 2 or 3, with 3 being relatively rare. You expect there to be occasional long runs of 1s or 2s (and less often 3s). That's what I observe from it. I'm using 2013b but I'd be surprised if something as fundamental as rand is broken in 2014a.

[dpb]

Indeed...a representative sample from looks like--

>> histc(floor(2.1*rand(1000,1))+1,[1:3])
ans =
 471
 490
  39
>> ans/sum(ans)
ans =
  0.4710
  0.4900
  0.0390
>>

[Dalas]

What I mean by stuck is that when I enter the value of x it get a singed a single value until I clear that definition of x. While the script does produce a variable value exactly like you described for some reason x ends up being a single set value.

[David Young]

Sounds like the problem is with the code that calls creature_state, not with creature_state itself. I think you need to show the relevant part of the calling code. (Best to edit the question to include it.)

Answer 1

[Image Analyst]

Did you know that floor rounds down to the nearest integer? If you want unique values, get rid of the floor. It has nothing to do with the version of MATLAB either of you are using.

[Dalas]

Yes I know. The script is called simple_creature its for a computational neuroscience class. Its meant to represent a system that has 3 states we have to make a script that can distinguish between these three states (with noise present).

[Image Analyst]

You can use randi(3, 1) to get a random number between 1 and 3. It's an integer though actually of class "double" rather than int32. It would be preferable than using that code you have.

[Image Analyst]

Regarding your comment above. It does not get stuck. Look at my test3.m where I call you function:

function test3
clc; % Clear command window.
x=creature_state()
x=creature_state()
x=creature_state()
x=creature_state()
x=creature_state()
x=creature_state()

function x=creature_state()
x=floor(2.1*rand)+1;
return

Now, look at the command window:

x =
     1
x =
     2
x =
     3
x =
     3
x =
     1
x =
     3

Do you see that x is always the same value every time? I don't.