How to prove that given quotation is not a distribution function











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I have function



$F(x,y)=begin{cases} 1, text{ if } x+y geq 0, \ 0, text{ if } x+y<0 end{cases}$.



I have no idea how can I prove that given quotation is not a distribution function. Only one think I know is $Delta_sF geq 0$.










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    up vote
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    down vote

    favorite












    I have function



    $F(x,y)=begin{cases} 1, text{ if } x+y geq 0, \ 0, text{ if } x+y<0 end{cases}$.



    I have no idea how can I prove that given quotation is not a distribution function. Only one think I know is $Delta_sF geq 0$.










    share|cite|improve this question


























      up vote
      0
      down vote

      favorite









      up vote
      0
      down vote

      favorite











      I have function



      $F(x,y)=begin{cases} 1, text{ if } x+y geq 0, \ 0, text{ if } x+y<0 end{cases}$.



      I have no idea how can I prove that given quotation is not a distribution function. Only one think I know is $Delta_sF geq 0$.










      share|cite|improve this question















      I have function



      $F(x,y)=begin{cases} 1, text{ if } x+y geq 0, \ 0, text{ if } x+y<0 end{cases}$.



      I have no idea how can I prove that given quotation is not a distribution function. Only one think I know is $Delta_sF geq 0$.







      probability probability-theory probability-distributions






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      edited Nov 26 at 8:37









      Tianlalu

      3,0001937




      3,0001937










      asked Nov 26 at 6:53









      Atstovas

      607




      607






















          1 Answer
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          $F(1,1)-F(1,-1)-F(-1,1)+F(-1,-1)=-1 <0$ so $F$ is not a distribution function. [In terms of random variable this means $P{-1<Xleq 1,-1<Yleq 1} <0$!].






          share|cite|improve this answer





















          • One more quostion. Why we take $-1$ instead $0$?
            – Atstovas
            Nov 26 at 13:37










          • I know that you used $Delta_s G= G(x_2,y_2)-G(x_1,y_2)-G(x_2,y_1)+G(x_1,y_1)$ From where I have to know how much $x_1,x_2,y_1,y_2$ is?
            – Atstovas
            Nov 26 at 13:47










          • @Atstovas If you take $0$ instead of $1$ you won't get a contradiction.
            – Kavi Rama Murthy
            Nov 26 at 23:17










          • so how to determine $x_1, x_2, y_1, y_2$ from given function $F(x,y)$?
            – Atstovas
            Nov 27 at 4:29












          • No thumb rule. You have to just play around with the function.
            – Kavi Rama Murthy
            Nov 27 at 5:27











          Your Answer





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          1 Answer
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          1 Answer
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          up vote
          0
          down vote



          accepted










          $F(1,1)-F(1,-1)-F(-1,1)+F(-1,-1)=-1 <0$ so $F$ is not a distribution function. [In terms of random variable this means $P{-1<Xleq 1,-1<Yleq 1} <0$!].






          share|cite|improve this answer





















          • One more quostion. Why we take $-1$ instead $0$?
            – Atstovas
            Nov 26 at 13:37










          • I know that you used $Delta_s G= G(x_2,y_2)-G(x_1,y_2)-G(x_2,y_1)+G(x_1,y_1)$ From where I have to know how much $x_1,x_2,y_1,y_2$ is?
            – Atstovas
            Nov 26 at 13:47










          • @Atstovas If you take $0$ instead of $1$ you won't get a contradiction.
            – Kavi Rama Murthy
            Nov 26 at 23:17










          • so how to determine $x_1, x_2, y_1, y_2$ from given function $F(x,y)$?
            – Atstovas
            Nov 27 at 4:29












          • No thumb rule. You have to just play around with the function.
            – Kavi Rama Murthy
            Nov 27 at 5:27















          up vote
          0
          down vote



          accepted










          $F(1,1)-F(1,-1)-F(-1,1)+F(-1,-1)=-1 <0$ so $F$ is not a distribution function. [In terms of random variable this means $P{-1<Xleq 1,-1<Yleq 1} <0$!].






          share|cite|improve this answer





















          • One more quostion. Why we take $-1$ instead $0$?
            – Atstovas
            Nov 26 at 13:37










          • I know that you used $Delta_s G= G(x_2,y_2)-G(x_1,y_2)-G(x_2,y_1)+G(x_1,y_1)$ From where I have to know how much $x_1,x_2,y_1,y_2$ is?
            – Atstovas
            Nov 26 at 13:47










          • @Atstovas If you take $0$ instead of $1$ you won't get a contradiction.
            – Kavi Rama Murthy
            Nov 26 at 23:17










          • so how to determine $x_1, x_2, y_1, y_2$ from given function $F(x,y)$?
            – Atstovas
            Nov 27 at 4:29












          • No thumb rule. You have to just play around with the function.
            – Kavi Rama Murthy
            Nov 27 at 5:27













          up vote
          0
          down vote



          accepted







          up vote
          0
          down vote



          accepted






          $F(1,1)-F(1,-1)-F(-1,1)+F(-1,-1)=-1 <0$ so $F$ is not a distribution function. [In terms of random variable this means $P{-1<Xleq 1,-1<Yleq 1} <0$!].






          share|cite|improve this answer












          $F(1,1)-F(1,-1)-F(-1,1)+F(-1,-1)=-1 <0$ so $F$ is not a distribution function. [In terms of random variable this means $P{-1<Xleq 1,-1<Yleq 1} <0$!].







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Nov 26 at 7:19









          Kavi Rama Murthy

          46.6k31854




          46.6k31854












          • One more quostion. Why we take $-1$ instead $0$?
            – Atstovas
            Nov 26 at 13:37










          • I know that you used $Delta_s G= G(x_2,y_2)-G(x_1,y_2)-G(x_2,y_1)+G(x_1,y_1)$ From where I have to know how much $x_1,x_2,y_1,y_2$ is?
            – Atstovas
            Nov 26 at 13:47










          • @Atstovas If you take $0$ instead of $1$ you won't get a contradiction.
            – Kavi Rama Murthy
            Nov 26 at 23:17










          • so how to determine $x_1, x_2, y_1, y_2$ from given function $F(x,y)$?
            – Atstovas
            Nov 27 at 4:29












          • No thumb rule. You have to just play around with the function.
            – Kavi Rama Murthy
            Nov 27 at 5:27


















          • One more quostion. Why we take $-1$ instead $0$?
            – Atstovas
            Nov 26 at 13:37










          • I know that you used $Delta_s G= G(x_2,y_2)-G(x_1,y_2)-G(x_2,y_1)+G(x_1,y_1)$ From where I have to know how much $x_1,x_2,y_1,y_2$ is?
            – Atstovas
            Nov 26 at 13:47










          • @Atstovas If you take $0$ instead of $1$ you won't get a contradiction.
            – Kavi Rama Murthy
            Nov 26 at 23:17










          • so how to determine $x_1, x_2, y_1, y_2$ from given function $F(x,y)$?
            – Atstovas
            Nov 27 at 4:29












          • No thumb rule. You have to just play around with the function.
            – Kavi Rama Murthy
            Nov 27 at 5:27
















          One more quostion. Why we take $-1$ instead $0$?
          – Atstovas
          Nov 26 at 13:37




          One more quostion. Why we take $-1$ instead $0$?
          – Atstovas
          Nov 26 at 13:37












          I know that you used $Delta_s G= G(x_2,y_2)-G(x_1,y_2)-G(x_2,y_1)+G(x_1,y_1)$ From where I have to know how much $x_1,x_2,y_1,y_2$ is?
          – Atstovas
          Nov 26 at 13:47




          I know that you used $Delta_s G= G(x_2,y_2)-G(x_1,y_2)-G(x_2,y_1)+G(x_1,y_1)$ From where I have to know how much $x_1,x_2,y_1,y_2$ is?
          – Atstovas
          Nov 26 at 13:47












          @Atstovas If you take $0$ instead of $1$ you won't get a contradiction.
          – Kavi Rama Murthy
          Nov 26 at 23:17




          @Atstovas If you take $0$ instead of $1$ you won't get a contradiction.
          – Kavi Rama Murthy
          Nov 26 at 23:17












          so how to determine $x_1, x_2, y_1, y_2$ from given function $F(x,y)$?
          – Atstovas
          Nov 27 at 4:29






          so how to determine $x_1, x_2, y_1, y_2$ from given function $F(x,y)$?
          – Atstovas
          Nov 27 at 4:29














          No thumb rule. You have to just play around with the function.
          – Kavi Rama Murthy
          Nov 27 at 5:27




          No thumb rule. You have to just play around with the function.
          – Kavi Rama Murthy
          Nov 27 at 5:27


















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