Probability generating function for random variable

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Homework Help Overview

The discussion revolves around a random variable X characterized by its probability generating function gX(s) = (5-4s²)⁻¹. Participants are attempting to calculate specific probabilities, P(X=3) and P(X=4), using the properties of the generating function.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants are exploring the implications of the generating function and its derivatives, questioning the values of g_X(0) and g'_X(0). There is also discussion about the series expansion of the generating function and its evaluation at s=0.

Discussion Status

There is an ongoing exploration of the generating function's properties, with some participants providing calculations for g_X(0) and its derivative. However, there is no clear consensus on the implications of these calculations, and some confusion remains regarding the evaluation of the series at s=0.

Contextual Notes

Participants are navigating the constraints of the problem, including the need to derive probabilities from the generating function without explicit solutions being provided. There is uncertainty about the interpretation of the generating function's properties and their application to the problem at hand.

tamintl
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Homework Statement


A random variable X has probability generating function gX(s) = (5-4s2)-1

Calculate P(X=3) and P(X=4)

Homework Equations


The Attempt at a Solution


Ehh don't really know where to go with one... I know:

gX(s) = E(sx) = Ʃ p(X=k)(sk)

Nit sure how to proceed..
Any help would be great!

Regards
Tam
 
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What is [itex]g_X(0)[/itex]?? What is [itex]g^\prime_X(0)[/itex]?? (the derivative)
 
micromass said:
What is [itex]g_X(0)[/itex]?? What is [itex]g^\prime_X(0)[/itex]?? (the derivative)

[itex]g_X(0)[/itex] = 5-1= 1/5
[itex]g^\prime_X(0)[/itex]= 0
 
Yes, and what if you calculate the same thing using

[tex]g_X(s)=\sum P\{X=k\}s^k[/tex]

??
 
micromass said:
Yes, and what if you calculate the same thing using

[tex]g_X(s)=\sum P\{X=k\}s^k[/tex]

??

Not sure what u mean but [tex]g_X(0)=\sum P\{X=3\}0^3[/tex]=0 ?
Sorry
 
tamintl said:
Not sure what you mean but [tex]g_X(0)=\sum P\{X=3\}0^3[/tex]=0 ?
Sorry

OK, if you have the series

[tex]P\{X=0\}+P\{X=1\}s+P\{X=2\}s^2+...[/tex]

what happens if I put s=0??
 
micromass said:
OK, if you have the series

[tex]P\{X=0\}+P\{X=1\}s+P\{X=2\}s^2+...[/tex]

what happens if I put s=0??

You will get '0'
 
tamintl said:
You will get '0'

No, you won't. Check again.
 
I'm not sure.. Sorry
 

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