Results 1 to 4 of 4

Thread: Poincare Map

  1. #1
    Super Member Showcase_22's Avatar
    Joined
    Sep 2006
    From
    The raggedy edge.
    Posts
    782

    Poincare Map

    I've got a rather long question, and i've done a lot of it, but i've hit a small hurdle and i'm not really sure what it wants me to work out.

    I have:

    $\displaystyle \dot{x_1}=x_1(x_2-x_3)$
    $\displaystyle \dot{x_2}=x_2(x_3-x_1)$
    $\displaystyle \dot{x_3}=x_3(x_1-x_2)$

    and i'm considering it's behaviour on the plane $\displaystyle x_1+x_2+x_3=1$.

    The question is this:

    On each line $\displaystyle x_i=0$, $\displaystyle i=1,2,3$ the dynamics can first be reduced to two equations in two variables (since $\displaystyle x_i$ is identically equal to 0), and then by using $\displaystyle x_1+x_2+x_3=1$, to one equation in one variable.

    Write down the equation and solve it.
    Find the Poincare map for a time step of t=1.
    Describe the dynamics on such a line.
    I decided to set $\displaystyle x_3=0$ so I would just be working in the $\displaystyle x_1, x_2$ plane.

    Substitutiing $\displaystyle x_3=0$ into the equations gives:

    $\displaystyle \dot{x_1}=x_1 x_2$
    $\displaystyle \dot{x_2}=-x_1 x_2$
    $\displaystyle \dot{x_3}=0$

    Then, using $\displaystyle x_1+x_2+x_3=1$ we get:

    $\displaystyle \dot{x_1}=x_1(1-x_1)$
    $\displaystyle \dot{x_2}=-x_2(1-x_2)$
    $\displaystyle \dot{x_3}=0$

    This shows that $\displaystyle x_3=0$ for all values of $\displaystyle x_1$ and $\displaystyle x_2$ (since it start at 0 and stays where it is).

    We can solve $\displaystyle x_1$ and $\displaystyle x_2$ to get:

    $\displaystyle x_1(t)=\frac{Ae^t}{1-Ae^t}$ and $\displaystyle x_2(t)=\frac{-Be^t}{1-Be^t}$ where A and B are constants.

    So my solution is:

    $\displaystyle \begin{pmatrix} {x_1} \\ {x_2} \end{pmatrix}=\begin{pmatrix} {\frac{Ae^t}{1-Ae^t}} \\ {\frac{-Be^t}{1-Be^t}} \end{pmatrix}$ <----- Is this right?

    So now I move on to try and find the Poincare map. I know that:

    $\displaystyle \begin{pmatrix} {\dot{x_1}} \\ {\dot{x_2}} \\ \dot{s} \end{pmatrix}=\begin{pmatrix} {x_1(1-x_1)} \\ {-x_2(1-x_2)} \\ 1 \end{pmatrix}$

    Now I have to make it $\displaystyle 2 \pi$ periodic so I get:

    $\displaystyle \begin{pmatrix} {\dot{x_1}} \\ {\dot{x_2}} \\ \dot{s} \end{pmatrix}=\begin{pmatrix} {x_1(1-x_1)} \\ {-x_2(1-x_2)+f(cos(2 \pi s))} \\ 1 \end{pmatrix}$

    From here I would just integrate the LHS, but I run into problems with $\displaystyle \dot{x_2}$. I tried choosing $\displaystyle f(cos( 2 \pi s))=cos(2 \pi s)$ but I still couldn't integrate that.

    Am I approaching the Poincare map in the correct way?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Dec 2010
    Posts
    2

    Modelling Nature's Nonlinearity?

    Hi, i couldn't help but notice this is part of the modelling nature's nonlinearity assignment?

    I was just wondering how far along you were and if you could help me because im struggling on it!

    Also, in regards to your question, i think you need ONE equation in ONE variable, not TWO as you have with x1 and x2? i hope this helps, you probably have your answer already anyway,

    If you could help, i would really appreciate it.

    Thank you!
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Jan 2011
    Posts
    1
    Tbh mate I haven't got a clue. Can you do the first question? All the notation is confusing me
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Dec 2010
    Posts
    2
    I cant do it either, its so much effort for what it is, im going to drop it for an unusual option or something! i mean if its this hard, i wonder how hard the next assignment is! ah well! sorry mate
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Poincare Maps
    Posted in the Differential Equations Forum
    Replies: 0
    Last Post: Mar 4th 2011, 11:11 AM
  2. Poincare Map
    Posted in the Differential Equations Forum
    Replies: 0
    Last Post: Nov 2nd 2009, 10:28 PM
  3. Poincare's Theorem
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: Sep 18th 2009, 12:24 PM
  4. Poincaré Conjecture
    Posted in the Math Forum
    Replies: 4
    Last Post: Aug 24th 2007, 04:46 AM
  5. Poincare conjecture
    Posted in the Math Forum
    Replies: 4
    Last Post: Aug 21st 2006, 03:31 PM

Search Tags


/mathhelpforum @mathhelpforum