How to find sum of random vectors (continuous and discrete)?












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After a search on the web I found this can be done with convolutions, though there was no such a topic in our class. Is there other way to solve this?



exercise










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    $begingroup$


    After a search on the web I found this can be done with convolutions, though there was no such a topic in our class. Is there other way to solve this?



    exercise










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      $begingroup$


      After a search on the web I found this can be done with convolutions, though there was no such a topic in our class. Is there other way to solve this?



      exercise










      share|cite|improve this question









      $endgroup$




      After a search on the web I found this can be done with convolutions, though there was no such a topic in our class. Is there other way to solve this?



      exercise







      probability probability-distributions






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      asked Jan 30 at 1:53









      Murad DavudovMurad Davudov

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          $begingroup$

          Any solution is going to be using convolutions, you just don't need to call them that.



          For example, in problem 4, $Z$ could be equal to $-1, 1, 2, 3,$ or $4$. For each one of those, you compute the probability $P(Z=z)$ by summing over all the possible cases that would lead to that, i.e. $(X,Y)=(x,y),; x+y = z$. In this case the only nontrivial one is
          $$P(Z=1) = P((X,Y) = (0,1)) + P((X,Y) = (2,-1)).$$



          Problem 5 is the same principle, but continuous. The CDF of $Z$, $G(z)$, is given by the integral of the given distribution over the region $x+y le z$, which is to say the area of that region intersected with the unit square. The PDF of $Z$ is the derivative of that, which will come out to be the length of the line $x+y=z$ intersected with the square.






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          • $begingroup$
            4th problem became clear to me, but I have problem grasping the idea of integral over that region. How is it denoted?
            $endgroup$
            – Murad Davudov
            Jan 30 at 5:28








          • 1




            $begingroup$
            $G(z) = int_{-infty}^z int_{-infty}^{z-y} f(x,y),dx,dy$
            $endgroup$
            – Nathaniel Mayer
            Jan 30 at 7:44












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          $begingroup$

          Any solution is going to be using convolutions, you just don't need to call them that.



          For example, in problem 4, $Z$ could be equal to $-1, 1, 2, 3,$ or $4$. For each one of those, you compute the probability $P(Z=z)$ by summing over all the possible cases that would lead to that, i.e. $(X,Y)=(x,y),; x+y = z$. In this case the only nontrivial one is
          $$P(Z=1) = P((X,Y) = (0,1)) + P((X,Y) = (2,-1)).$$



          Problem 5 is the same principle, but continuous. The CDF of $Z$, $G(z)$, is given by the integral of the given distribution over the region $x+y le z$, which is to say the area of that region intersected with the unit square. The PDF of $Z$ is the derivative of that, which will come out to be the length of the line $x+y=z$ intersected with the square.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            4th problem became clear to me, but I have problem grasping the idea of integral over that region. How is it denoted?
            $endgroup$
            – Murad Davudov
            Jan 30 at 5:28








          • 1




            $begingroup$
            $G(z) = int_{-infty}^z int_{-infty}^{z-y} f(x,y),dx,dy$
            $endgroup$
            – Nathaniel Mayer
            Jan 30 at 7:44
















          1












          $begingroup$

          Any solution is going to be using convolutions, you just don't need to call them that.



          For example, in problem 4, $Z$ could be equal to $-1, 1, 2, 3,$ or $4$. For each one of those, you compute the probability $P(Z=z)$ by summing over all the possible cases that would lead to that, i.e. $(X,Y)=(x,y),; x+y = z$. In this case the only nontrivial one is
          $$P(Z=1) = P((X,Y) = (0,1)) + P((X,Y) = (2,-1)).$$



          Problem 5 is the same principle, but continuous. The CDF of $Z$, $G(z)$, is given by the integral of the given distribution over the region $x+y le z$, which is to say the area of that region intersected with the unit square. The PDF of $Z$ is the derivative of that, which will come out to be the length of the line $x+y=z$ intersected with the square.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            4th problem became clear to me, but I have problem grasping the idea of integral over that region. How is it denoted?
            $endgroup$
            – Murad Davudov
            Jan 30 at 5:28








          • 1




            $begingroup$
            $G(z) = int_{-infty}^z int_{-infty}^{z-y} f(x,y),dx,dy$
            $endgroup$
            – Nathaniel Mayer
            Jan 30 at 7:44














          1












          1








          1





          $begingroup$

          Any solution is going to be using convolutions, you just don't need to call them that.



          For example, in problem 4, $Z$ could be equal to $-1, 1, 2, 3,$ or $4$. For each one of those, you compute the probability $P(Z=z)$ by summing over all the possible cases that would lead to that, i.e. $(X,Y)=(x,y),; x+y = z$. In this case the only nontrivial one is
          $$P(Z=1) = P((X,Y) = (0,1)) + P((X,Y) = (2,-1)).$$



          Problem 5 is the same principle, but continuous. The CDF of $Z$, $G(z)$, is given by the integral of the given distribution over the region $x+y le z$, which is to say the area of that region intersected with the unit square. The PDF of $Z$ is the derivative of that, which will come out to be the length of the line $x+y=z$ intersected with the square.






          share|cite|improve this answer









          $endgroup$



          Any solution is going to be using convolutions, you just don't need to call them that.



          For example, in problem 4, $Z$ could be equal to $-1, 1, 2, 3,$ or $4$. For each one of those, you compute the probability $P(Z=z)$ by summing over all the possible cases that would lead to that, i.e. $(X,Y)=(x,y),; x+y = z$. In this case the only nontrivial one is
          $$P(Z=1) = P((X,Y) = (0,1)) + P((X,Y) = (2,-1)).$$



          Problem 5 is the same principle, but continuous. The CDF of $Z$, $G(z)$, is given by the integral of the given distribution over the region $x+y le z$, which is to say the area of that region intersected with the unit square. The PDF of $Z$ is the derivative of that, which will come out to be the length of the line $x+y=z$ intersected with the square.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Jan 30 at 2:57









          Nathaniel MayerNathaniel Mayer

          1,863516




          1,863516












          • $begingroup$
            4th problem became clear to me, but I have problem grasping the idea of integral over that region. How is it denoted?
            $endgroup$
            – Murad Davudov
            Jan 30 at 5:28








          • 1




            $begingroup$
            $G(z) = int_{-infty}^z int_{-infty}^{z-y} f(x,y),dx,dy$
            $endgroup$
            – Nathaniel Mayer
            Jan 30 at 7:44


















          • $begingroup$
            4th problem became clear to me, but I have problem grasping the idea of integral over that region. How is it denoted?
            $endgroup$
            – Murad Davudov
            Jan 30 at 5:28








          • 1




            $begingroup$
            $G(z) = int_{-infty}^z int_{-infty}^{z-y} f(x,y),dx,dy$
            $endgroup$
            – Nathaniel Mayer
            Jan 30 at 7:44
















          $begingroup$
          4th problem became clear to me, but I have problem grasping the idea of integral over that region. How is it denoted?
          $endgroup$
          – Murad Davudov
          Jan 30 at 5:28






          $begingroup$
          4th problem became clear to me, but I have problem grasping the idea of integral over that region. How is it denoted?
          $endgroup$
          – Murad Davudov
          Jan 30 at 5:28






          1




          1




          $begingroup$
          $G(z) = int_{-infty}^z int_{-infty}^{z-y} f(x,y),dx,dy$
          $endgroup$
          – Nathaniel Mayer
          Jan 30 at 7:44




          $begingroup$
          $G(z) = int_{-infty}^z int_{-infty}^{z-y} f(x,y),dx,dy$
          $endgroup$
          – Nathaniel Mayer
          Jan 30 at 7:44


















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