determine the stability of an equilibrium point(x,0).











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I would like to determine the stability of equilibrium point $(x,0)$ of the differential equation



$dot x = Ax$



$ A=
bigg[
begin{matrix}
0&0\0&a
end{matrix}
bigg]
$
and $ a >0 $



I got
$ x'(t) = 0 $
$ y'(t) = a*y$



So, the equilibrium point is $(x,0)$.



How can I determine the stability of these equilibrium points?



Here is the phase portrait:



Any help will be appreciated!










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  • The entire $x$ axis is an equilibrium point.
    – copper.hat
    Nov 15 at 1:50










  • @Moo I draw the phase portrait, and I think the equilibrium point is unstable.
    – HIABCD
    Nov 15 at 17:33












  • Thanks! Please add.
    – HIABCD
    Nov 15 at 17:49















up vote
1
down vote

favorite
1












I would like to determine the stability of equilibrium point $(x,0)$ of the differential equation



$dot x = Ax$



$ A=
bigg[
begin{matrix}
0&0\0&a
end{matrix}
bigg]
$
and $ a >0 $



I got
$ x'(t) = 0 $
$ y'(t) = a*y$



So, the equilibrium point is $(x,0)$.



How can I determine the stability of these equilibrium points?



Here is the phase portrait:



Any help will be appreciated!










share|cite|improve this question
























  • The entire $x$ axis is an equilibrium point.
    – copper.hat
    Nov 15 at 1:50










  • @Moo I draw the phase portrait, and I think the equilibrium point is unstable.
    – HIABCD
    Nov 15 at 17:33












  • Thanks! Please add.
    – HIABCD
    Nov 15 at 17:49













up vote
1
down vote

favorite
1









up vote
1
down vote

favorite
1






1





I would like to determine the stability of equilibrium point $(x,0)$ of the differential equation



$dot x = Ax$



$ A=
bigg[
begin{matrix}
0&0\0&a
end{matrix}
bigg]
$
and $ a >0 $



I got
$ x'(t) = 0 $
$ y'(t) = a*y$



So, the equilibrium point is $(x,0)$.



How can I determine the stability of these equilibrium points?



Here is the phase portrait:



Any help will be appreciated!










share|cite|improve this question















I would like to determine the stability of equilibrium point $(x,0)$ of the differential equation



$dot x = Ax$



$ A=
bigg[
begin{matrix}
0&0\0&a
end{matrix}
bigg]
$
and $ a >0 $



I got
$ x'(t) = 0 $
$ y'(t) = a*y$



So, the equilibrium point is $(x,0)$.



How can I determine the stability of these equilibrium points?



Here is the phase portrait:



Any help will be appreciated!







calculus differential-equations stability-theory






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share|cite|improve this question













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share|cite|improve this question








edited Nov 15 at 17:37

























asked Nov 15 at 1:48









HIABCD

83




83












  • The entire $x$ axis is an equilibrium point.
    – copper.hat
    Nov 15 at 1:50










  • @Moo I draw the phase portrait, and I think the equilibrium point is unstable.
    – HIABCD
    Nov 15 at 17:33












  • Thanks! Please add.
    – HIABCD
    Nov 15 at 17:49


















  • The entire $x$ axis is an equilibrium point.
    – copper.hat
    Nov 15 at 1:50










  • @Moo I draw the phase portrait, and I think the equilibrium point is unstable.
    – HIABCD
    Nov 15 at 17:33












  • Thanks! Please add.
    – HIABCD
    Nov 15 at 17:49
















The entire $x$ axis is an equilibrium point.
– copper.hat
Nov 15 at 1:50




The entire $x$ axis is an equilibrium point.
– copper.hat
Nov 15 at 1:50












@Moo I draw the phase portrait, and I think the equilibrium point is unstable.
– HIABCD
Nov 15 at 17:33






@Moo I draw the phase portrait, and I think the equilibrium point is unstable.
– HIABCD
Nov 15 at 17:33














Thanks! Please add.
– HIABCD
Nov 15 at 17:49




Thanks! Please add.
– HIABCD
Nov 15 at 17:49










1 Answer
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We want to determine the stability of the equilibrium points of the system $dot x = Ax$, where



$$ A=
bigg[
begin{matrix}
0&0\0&a
end{matrix}
bigg], ~text{with}~a >0 $$



The critical points are where we simultaneously have $x' = y' = 0$ and we get the entire $x-$axis as



$$(x, y) = (x, 0)$$



Since this system is decoupled, we can write
$$begin{align} x'(t) &= 0 implies x(t) = c \ y'(t) &= ay implies y(t) = c e^{a t} end{align}$$



The phase portrait is



enter image description here



Using all of the information above, we determine that the critical point is unstable.






share|cite|improve this answer























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    1 Answer
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    active

    oldest

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    up vote
    0
    down vote



    accepted










    We want to determine the stability of the equilibrium points of the system $dot x = Ax$, where



    $$ A=
    bigg[
    begin{matrix}
    0&0\0&a
    end{matrix}
    bigg], ~text{with}~a >0 $$



    The critical points are where we simultaneously have $x' = y' = 0$ and we get the entire $x-$axis as



    $$(x, y) = (x, 0)$$



    Since this system is decoupled, we can write
    $$begin{align} x'(t) &= 0 implies x(t) = c \ y'(t) &= ay implies y(t) = c e^{a t} end{align}$$



    The phase portrait is



    enter image description here



    Using all of the information above, we determine that the critical point is unstable.






    share|cite|improve this answer



























      up vote
      0
      down vote



      accepted










      We want to determine the stability of the equilibrium points of the system $dot x = Ax$, where



      $$ A=
      bigg[
      begin{matrix}
      0&0\0&a
      end{matrix}
      bigg], ~text{with}~a >0 $$



      The critical points are where we simultaneously have $x' = y' = 0$ and we get the entire $x-$axis as



      $$(x, y) = (x, 0)$$



      Since this system is decoupled, we can write
      $$begin{align} x'(t) &= 0 implies x(t) = c \ y'(t) &= ay implies y(t) = c e^{a t} end{align}$$



      The phase portrait is



      enter image description here



      Using all of the information above, we determine that the critical point is unstable.






      share|cite|improve this answer

























        up vote
        0
        down vote



        accepted







        up vote
        0
        down vote



        accepted






        We want to determine the stability of the equilibrium points of the system $dot x = Ax$, where



        $$ A=
        bigg[
        begin{matrix}
        0&0\0&a
        end{matrix}
        bigg], ~text{with}~a >0 $$



        The critical points are where we simultaneously have $x' = y' = 0$ and we get the entire $x-$axis as



        $$(x, y) = (x, 0)$$



        Since this system is decoupled, we can write
        $$begin{align} x'(t) &= 0 implies x(t) = c \ y'(t) &= ay implies y(t) = c e^{a t} end{align}$$



        The phase portrait is



        enter image description here



        Using all of the information above, we determine that the critical point is unstable.






        share|cite|improve this answer














        We want to determine the stability of the equilibrium points of the system $dot x = Ax$, where



        $$ A=
        bigg[
        begin{matrix}
        0&0\0&a
        end{matrix}
        bigg], ~text{with}~a >0 $$



        The critical points are where we simultaneously have $x' = y' = 0$ and we get the entire $x-$axis as



        $$(x, y) = (x, 0)$$



        Since this system is decoupled, we can write
        $$begin{align} x'(t) &= 0 implies x(t) = c \ y'(t) &= ay implies y(t) = c e^{a t} end{align}$$



        The phase portrait is



        enter image description here



        Using all of the information above, we determine that the critical point is unstable.







        share|cite|improve this answer














        share|cite|improve this answer



        share|cite|improve this answer








        edited Nov 15 at 18:45

























        answered Nov 15 at 18:30









        Moo

        5,2883920




        5,2883920






























             

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