Derive mgf bivariate normal distribution

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SUMMARY

The joint moment generating function (mgf) for bivariate normal distributions is defined as MX,Y(s,t) = E(exs + yt). The correct approach involves expanding the exponential in a power series and integrating under the integral sign. The bivariate normal density function fXY(x,y) is given by (1/(2π√(1-ρ2σxσy))) exp[-(1/2(1-ρ2))((x-μxx)2 + (y-μyy)2 - 2ρ(x-μxx)(y-μyy))]. This method leads to the derivation of the mgf for bivariate normal distributions.

PREREQUISITES
  • Bivariate normal distribution theory
  • Moment generating functions (mgf)
  • Power series expansion
  • Double integration techniques
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Lewis7879
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Does anyone know the proof of joint moment generating functions for bivariate normal distributions?
M_x,y (s,t)= E(e^(xs+yt))
 
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Expand the exponential in a power series. E(each term) is that moment.
 
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mathman said:
Expand the exponential in a power series. E(each term) is that moment.
I'm actually suppose to do it like
mathman said:
Expand the exponential in a power series. E(each term) is that moment.
great idea
it is possible to do it this way ?
its a very long step.
M(s,t)= e(xs+yt) ∫∫ fXY (x,y) dxdy
= e(xs+yt) ∫∫ (1/(2π√(1-ρ2xσy)) exp [ [-1/2(1-ρ2)] [(x-μxx)2 + (y-μyy)2 - 2ρ(x-μxx)(y-μyy)}
 
Lewis7879 said:
I'm actually suppose to do it like

great idea
it is possible to do it this way ?
its a very long step.
M(s,t)= e(xs+yt) ∫∫ fXY (x,y) dxdy
= e(xs+yt) ∫∫ (1/(2π√(1-ρ2xσy)) exp [ [-1/2(1-ρ2)] [(x-μxx)2 + (y-μyy)2 - 2ρ(x-μxx)(y-μyy)}
No. e^{(xs+yt)} must be under the integral sign.
 
  • Like
Likes   Reactions: Lewis7879
mathman said:
Expand the exponential in a power series. E(each term) is that moment.
I'm actually suppose to do it like
M(s,t)=
mathman said:
No. e^{(xs+yt)} must be under the integral sign.
yes I know that but will I get the solution of mgf of bivariate normal distribution ? I'm stuck current trying to derive it.
 
Lewis7879 said:
I'm actually suppose to do it like
M(s,t)=

yes I know that but will I get the solution of mgf of bivariate normal distribution ? I'm stuck current trying to derive it.
That will depend on what f_{XY}(x,y) is. If it is bivariate normal, then you will get its moment generating function.
 

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