Determine the joint density function $f(x,y)$ for $0<y0$












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The continuous random variables X and Y have the joint distribution function
$$F(x,y)=begin{cases}1-e^{-x} & y>1 ,:x>0\y(1-e^{-x}) & 0<y<1,:x > 0\0 & elseend{cases}$$
Determine the joint density function $f(x,y)$ for $0<y<1$ and $x>0$




Usually to go from the distribution function to the density function I differentiate the distribution function, but in this case I have the joint so it depends on $x$ and $y$, how can I calculate the joint density function? Also because the interval $x>0$ is present in $2$ cases, how can I deal with?










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    0












    $begingroup$



    The continuous random variables X and Y have the joint distribution function
    $$F(x,y)=begin{cases}1-e^{-x} & y>1 ,:x>0\y(1-e^{-x}) & 0<y<1,:x > 0\0 & elseend{cases}$$
    Determine the joint density function $f(x,y)$ for $0<y<1$ and $x>0$




    Usually to go from the distribution function to the density function I differentiate the distribution function, but in this case I have the joint so it depends on $x$ and $y$, how can I calculate the joint density function? Also because the interval $x>0$ is present in $2$ cases, how can I deal with?










    share|cite|improve this question









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      0












      0








      0





      $begingroup$



      The continuous random variables X and Y have the joint distribution function
      $$F(x,y)=begin{cases}1-e^{-x} & y>1 ,:x>0\y(1-e^{-x}) & 0<y<1,:x > 0\0 & elseend{cases}$$
      Determine the joint density function $f(x,y)$ for $0<y<1$ and $x>0$




      Usually to go from the distribution function to the density function I differentiate the distribution function, but in this case I have the joint so it depends on $x$ and $y$, how can I calculate the joint density function? Also because the interval $x>0$ is present in $2$ cases, how can I deal with?










      share|cite|improve this question









      $endgroup$





      The continuous random variables X and Y have the joint distribution function
      $$F(x,y)=begin{cases}1-e^{-x} & y>1 ,:x>0\y(1-e^{-x}) & 0<y<1,:x > 0\0 & elseend{cases}$$
      Determine the joint density function $f(x,y)$ for $0<y<1$ and $x>0$




      Usually to go from the distribution function to the density function I differentiate the distribution function, but in this case I have the joint so it depends on $x$ and $y$, how can I calculate the joint density function? Also because the interval $x>0$ is present in $2$ cases, how can I deal with?







      probability statistics






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      asked Jan 26 at 17:15









      Luke MarciLuke Marci

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          $begingroup$

          You simply differentiate with respect to both variables, i.e. $$frac{partial F(x,y)}{partial x partial y}=begin{cases}0 & y>1 ,:x>0\e^{-x} & 0<y<1,:x > 0\0 & elseend{cases}$$
          The answer might seem counter-intuitive but inspect the joint CDF. When $y>1$, $F(x,y)=P(Xleq x, Y leq y)$ doesn't change with respect to $y$, i.e. there is no volume for $y$, when $y>1$.






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          • $begingroup$
            You are right, thank you a lot for the answer! :)
            $endgroup$
            – Luke Marci
            Jan 26 at 18:44











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          1 Answer
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          1 Answer
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          1












          $begingroup$

          You simply differentiate with respect to both variables, i.e. $$frac{partial F(x,y)}{partial x partial y}=begin{cases}0 & y>1 ,:x>0\e^{-x} & 0<y<1,:x > 0\0 & elseend{cases}$$
          The answer might seem counter-intuitive but inspect the joint CDF. When $y>1$, $F(x,y)=P(Xleq x, Y leq y)$ doesn't change with respect to $y$, i.e. there is no volume for $y$, when $y>1$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            You are right, thank you a lot for the answer! :)
            $endgroup$
            – Luke Marci
            Jan 26 at 18:44
















          1












          $begingroup$

          You simply differentiate with respect to both variables, i.e. $$frac{partial F(x,y)}{partial x partial y}=begin{cases}0 & y>1 ,:x>0\e^{-x} & 0<y<1,:x > 0\0 & elseend{cases}$$
          The answer might seem counter-intuitive but inspect the joint CDF. When $y>1$, $F(x,y)=P(Xleq x, Y leq y)$ doesn't change with respect to $y$, i.e. there is no volume for $y$, when $y>1$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            You are right, thank you a lot for the answer! :)
            $endgroup$
            – Luke Marci
            Jan 26 at 18:44














          1












          1








          1





          $begingroup$

          You simply differentiate with respect to both variables, i.e. $$frac{partial F(x,y)}{partial x partial y}=begin{cases}0 & y>1 ,:x>0\e^{-x} & 0<y<1,:x > 0\0 & elseend{cases}$$
          The answer might seem counter-intuitive but inspect the joint CDF. When $y>1$, $F(x,y)=P(Xleq x, Y leq y)$ doesn't change with respect to $y$, i.e. there is no volume for $y$, when $y>1$.






          share|cite|improve this answer









          $endgroup$



          You simply differentiate with respect to both variables, i.e. $$frac{partial F(x,y)}{partial x partial y}=begin{cases}0 & y>1 ,:x>0\e^{-x} & 0<y<1,:x > 0\0 & elseend{cases}$$
          The answer might seem counter-intuitive but inspect the joint CDF. When $y>1$, $F(x,y)=P(Xleq x, Y leq y)$ doesn't change with respect to $y$, i.e. there is no volume for $y$, when $y>1$.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Jan 26 at 18:34









          gunesgunes

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          3747












          • $begingroup$
            You are right, thank you a lot for the answer! :)
            $endgroup$
            – Luke Marci
            Jan 26 at 18:44


















          • $begingroup$
            You are right, thank you a lot for the answer! :)
            $endgroup$
            – Luke Marci
            Jan 26 at 18:44
















          $begingroup$
          You are right, thank you a lot for the answer! :)
          $endgroup$
          – Luke Marci
          Jan 26 at 18:44




          $begingroup$
          You are right, thank you a lot for the answer! :)
          $endgroup$
          – Luke Marci
          Jan 26 at 18:44


















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