PlanetMath (more info)
 Math for the people, by the people. Sponsor PlanetMath
Encyclopedia | Requests | Forums | Docs | Wiki | Random | RSS  
Login
create new user
name:
pass:
forget your password?
Main Menu
Owner confidence rating: Low Entry average rating: No information on entry rating
[parent] moment generating function of the sum of independent random variables (Corollary)

Let $X_i$ be independent random variables for $ i=1,\dotsc ,n$ , let each $X_i$ have moment generating function $M_{X_i} (t)$ , and let $X=\sum_{i=1}^n X_i$ . Then the moment generating function of $X$ is $$ M_X(t)=\prod_{i=1}^n M_{X_i}(t) $$

Proof. By definition,
$\displaystyle M_X(t)$ $\displaystyle =E\left(\mathrm{e}^{tX}\right)$    
  $\displaystyle =E\left(\mathrm{e}^{t\left(X_1+\dotsb+X_n\right)}\right)$    
  $\displaystyle =E\left(\mathrm{e}^{tX_1}\dotsm\mathrm{e}^{tX_n}\right) .$    

Now, since each $X_i$ is independent of the others, this becomes
$\displaystyle M_X(t)$ $\displaystyle =E\left(\mathrm{e}^{tX_1}\right)\dotsm E\left(\mathrm{e}^{tX_n}\right)$    
  $\displaystyle =M_{X_1}(t)\dotsm M_{X_n}(t)$    
  $\displaystyle =\prod_{i=1}^n M_{X_i}(t)$    

as required. $ \qedsymbol$




"moment generating function of the sum of independent random variables" is owned by me_and. [ full author list (2) ]
(view preamble | get metadata)

View style:


This object's parent.
Log in to rate this entry.
(view current ratings)

Cross-references: moment generating function, random variables, independent

This is version 2 of moment generating function of the sum of independent random variables, born on 2007-06-20, modified 2007-06-23.
Object id is 9628, canonical name is MomentGeneratingFunctionOfTheSumOfIndepententRandomVariables.
Accessed 1478 times total.

Classification:
AMS MSC60E05 (Probability theory and stochastic processes :: Distribution theory :: Distributions: general theory)

Pending Errata and Addenda
None.
Discussion
Style: Expand: Order:
forum policy

No messages.

Interact
post | correct | update request | add example | add (any)