How do I get prctile function to work?

Here is my code for what I am trying to do:

Iterations = 5000;

for i = 1:Iterations
format rat; 
Beta = 8/13; 
U = rand(1); 
condition1 = U <= 8/13; 
T(condition1) = sqrt(8*U/13);
condition2 = U > 8/13; 
T(condition2) = 1 - sqrt(5*(1 - U)/13);
N = floor(80 + 130*T); 
Zmatrix = floor(170 + 316*rand(1,N)); 
x(i) = sum(Zmatrix); 

end

hist(x)
m = mean(x)
v = var(x)

prctile(x,25)

Basically, I have created an array of value x, and successfully created a histogram from the data. However, the prctile(x,25) function is not working.

What do I have to do to get Matlab to understand the prctile function? I have version 7.12.0 (R2011a). Any ideas?

[the cyclist]

Can you be more specific by what you mean by "not working"? Give the full error message if you get one. If it runs, but gives a value that you think is wrong, please explain why.

[Jonathan]

The message I get in the Command Window when I try to run the code is:

??? Undefined function or method 'prctile' for input arguments of type 'double'.

Error in ==> m_file_hw1_problem3 at 21 prctile(x,25)

So I am not getting a value at all. It just gives me this error message.

Answer 1

[the cyclist]

prctile() is a function in the Statistics Toolbox. Type

ver

at the command prompt to see your list of available toolboxes.

[Jonathan]

It seems I only have the signal processing toolbox:

MATLAB Version 7.12 (R2011a) Signal Processing Toolbox Version 6.15 (R2011a)

So that is probably the issue right? Is there a way to program a toolbox like prctile() into Matlab?

[the cyclist]

That is definitely the issue.

Your options:

• Buy the Statistics Toolbox
• Program this one function yourself
• Look in the File Exchange to see if someone has contributed a percentile function that you could download and use.

Each of these options has pros and cons, depending on your knowledge, wealth, and time available.

[Jonathan]

Okay, thank you very much!

Answer 2

[the cyclist]

I don't know why you chose

format rat

which I am going to ignore for now.

I get that

m = 4.8e4

and

prctile(x,25) = 4.3e4

(approximately).

Both of these values look quite reasonable, given your histogram. Do you get something different? I am running R2013a.

[Jonathan]

Oops, I meant to post my reply here. Not sure if it matters...

The message I get in the Command Window when I try to run the code is:

??? Undefined function or method 'prctile' for input arguments of type 'double'.

Error in ==> m_file_hw1_problem3 at 21 prctile(x,25)

So I am not getting a value at all. It just gives me this error message.