Probability generating function

In summary, the conversation discusses a random variable X and its generating function. The main question is how to calculate the expected value and variance of X using the generating function. The conversation also touches on the difference between moment generating functions and probability generating functions, and the applicability of these formulas to different probability distributions. Finally, the solution to calculating E(X) and Var(X) using the generating function is provided.
  • #1
elmarsur
36
0

Homework Statement



A random variable X has the generating function
f(z) = 1 / (2-z)^2
Find E(X) and Var(X).


Homework Equations





The Attempt at a Solution



Would anyone explain in simpler terms the notion of the generating function, such that I may be able to solve problems? All I have found were proofs, but nothing of practical use.

Thank you very much!
 
Physics news on Phys.org
  • #2
Thank you very much, LC!

I imagine that there isn't any significant difference between MGF and PGF (probability), the latter being a special application of the first?!
If so, I still have a couple of questions:
1) Do the formulae apply to all sorts of probability distributions/densities?
2) How do I calculate the variance (formula-wise) for these generating functions (which I understand are not really functions but series of terms)?

Thank you very much in advance.
 
  • #3
elmarsur said:
Thank you very much, LC!

I imagine that there isn't any significant difference between MGF and PGF (probability), the latter being a special application of the first?!
If so, I still have a couple of questions:
1) Do the formulae apply to all sorts of probability distributions/densities?
2) How do I calculate the variance (formula-wise) for these generating functions (which I understand are not really functions but series of terms)?

Thank you very much in advance.

I posted that reply quickly as I was about to leave for a movie and hadn't noticed you were asking about a probability generating function instead of moment generating function. I deleted the post but apparently you saw it before I deleted it. PGF's are defined for non-negative integer valued random variables. For a PGF PX(z),

E(X) = P'X(1) and
Var(X) = P''X(1) + P'X(1) - (P'X(1))2
 
Last edited:
  • #4
Thank you very much, LC!
I hope I find you around again when I cry for help.
 

Related to Probability generating function

What is a probability generating function?

A probability generating function is a mathematical tool used to describe the probability distribution of a discrete random variable. It is a power series that represents the probabilities of all possible outcomes of the random variable.

How is a probability generating function different from a moment generating function?

A probability generating function is specific to discrete random variables, while a moment generating function can be used for both discrete and continuous random variables. Additionally, the coefficients in a probability generating function represent probabilities, while the coefficients in a moment generating function represent moments of the random variable.

What is the purpose of using a probability generating function?

A probability generating function allows us to easily calculate various properties of a discrete random variable, such as its expected value and variance. It also allows us to determine the probability of specific outcomes or events occurring.

How do you calculate the probability generating function for a given random variable?

The probability generating function is calculated by taking the sum of pixi for all possible values of the random variable, where pi is the probability of the random variable taking on the value i. This can also be expressed as the expected value of xs, where s is a variable.

Can a probability generating function be used for continuous random variables?

No, a probability generating function can only be used for discrete random variables. For continuous random variables, we use a moment generating function or a probability density function to describe the probability distribution.

Similar threads

  • Calculus and Beyond Homework Help
Replies
17
Views
1K
  • Calculus and Beyond Homework Help
Replies
27
Views
779
  • Calculus and Beyond Homework Help
Replies
3
Views
1K
  • Calculus and Beyond Homework Help
Replies
2
Views
1K
  • Calculus and Beyond Homework Help
Replies
8
Views
511
  • Calculus and Beyond Homework Help
Replies
9
Views
2K
  • Calculus and Beyond Homework Help
Replies
1
Views
1K
  • Calculus and Beyond Homework Help
Replies
7
Views
583
  • Calculus and Beyond Homework Help
Replies
7
Views
352
  • Calculus and Beyond Homework Help
Replies
8
Views
1K
Back
Top