How Do You Find the PDF of Z=X+Y When X and Y Are Not Independent?

  • Thread starter Thread starter joserse46
  • Start date Start date
  • Tags Tags
    Sum
AI Thread Summary
To find the PDF of Z=X+Y when X and Y are not independent, the joint PDF f(x,y) is given as f(x,y) = (1/x) for 0≤y≤x≤1. The cumulative distribution function F(z) is defined as F(z) = P(Z≤z) = ∫∫fXY(x,y) dx dy with specific limits. The differentiation to find the PDF f(z) involves using Leibnitz's rule, but the integral does not converge, indicating potential issues with the validity of f(x,y) as a PDF. The discussion highlights the complexities of working with dependent random variables and suggests that the problem may be more suited for a homework forum.
joserse46
Messages
4
Reaction score
0
f(x,y) = (1/x) for 0≤y≤x≤1

A new rv Z=X+Y where X,Y not independent find the pdf of z

My approach

F(z) = P(Z≤z) = ∫∫fXY(x,y) dx dy x= -∞ to ∞ y= 0 to z-y

f(z) = d/dz(F(z)) = ∫fXY(z-y,y) dy y= -∞ to ∞ (using Leibnitz)

where i am stuck is this doesn't converge
 
Physics news on Phys.org
(this thread belongs in the homework forums)

f(x,y) might not be a valid pdf
 
I was reading documentation about the soundness and completeness of logic formal systems. Consider the following $$\vdash_S \phi$$ where ##S## is the proof-system making part the formal system and ##\phi## is a wff (well formed formula) of the formal language. Note the blank on left of the turnstile symbol ##\vdash_S##, as far as I can tell it actually represents the empty set. So what does it mean ? I guess it actually means ##\phi## is a theorem of the formal system, i.e. there is a...
Back
Top