What is the code?

I want to generate random numbers. But i want it like this. for example i want to generate random numbers for The gamma distribution coefficient of skewness 2.

How can i do this?

Answer 1

[José-Luis]

 doc gamrnd

The skewness is a function of one of the two parameters of the distribution, that you can set as you see fit. You just need to set it so the skewness is two (look at the wikipedia article on the gamma distribution).

[eren eren]

Sorry i dont understand. what is doc gamrnd ?

[José-Luis]

There is already a function that does what you ask. Look at the documentation for gamrnd

I was suggesting that you type doc gamrnd in the prompt to browse the documentation. Read it and you'll hopefully understand.

[eren eren]

no i understood that but in gamrnd don't have skewness a place to enter.

[José-Luis]

From one of your comments.

When you do this:

i write this on matlab skewness = 2; scale = 1; shape = 2./sqrt(skewness); x=gamrnd(shape,scale) s=skewness(x)

Skewness becomes a variable, and overshadows the built-in skewness function in Matlab. It is good practice not to do that, as problems as the one got might pop-up (you think you are calling a function but you are in fact trying to access a variable).

After clearing your work space to make sure there is no variable called skweness in it, do this instead:

 ske = 2;
 sca = 1;
 shap = 1/sqrt(2);
 x = gamrnd(shap,sca,[1000 1]);
 your_skew = skewness(x);

Please accept an answer if it helped you.

[eren eren]

yes it is working. can i use this, beta, chi squre etc. distributions?

Answer 2

[Jonathan Sullivan]

skewness is simple 2 divided by the square root of the shape parameter for gamma distributions. Here's an example.

skewness = 2;
scale = 1;
shape = 2./sqrt(skewness);
gamrnd(shape,scale)

[eren eren]

if i use this, do the random numbers of gamma distrubition have the 2 skewness?

[eren eren]

This isn't working

[José-Luis]

It is not working how?

[eren eren]

i generated numbers but i dont be sure skewness=2. x=gamrnd(shape,scale) and i use A=skewness(x) code, the code not working.

[José-Luis]

Since it's a random sample, it might not be exactly equal to 2. Also, there might be some bias. "The code not working" is not a very useful statement for those that are trying to help you. An example showing what you get/what you expect would be more helpful.

[eren eren]

no no, the skewness code does not works. it returns an error. i know there might be some bias

[José-Luis]

What does your code look like? And the error is? It is hard to help you without details.

[eren eren]

i write this on matlab skewness = 2; scale = 1; shape = 2./sqrt(skewness); x=gamrnd(shape,scale) s=skewness(x)

and error is;

??? Attempted to access skewness(0.412164); index must be a positive integer or logical.

[José-Luis]

Please see the comment to my original answer.