# Henon Map Fixed Points Plot versus Iterations and Plot of the Map

For the Henon Map: $$x_{n+1}=y_n+1-αx_n^2, \quad y_{n+1}=β x_n$$ I would like to discover period doubling bifurcations by varying the parameter $α$ and plotting $x_n,y_n$ versus the iterations $n$ of the map and then print below the values of the points in order to distinguish period cycles.

For one dimensional systems of the form $x_{n+1}=f(x_n)$ the period-$2$ cycles happen when the system: $$x_1=f(x_2) \\ x_2=f(x_1)$$ has a unique solution. In other words, the trajetory "jumps" between $x_1$ and $x_2$ so while iterating the map they keep appearing (until a certain value of the parameter of the system). I have managed to do something similar for the map

$$x_{n+1}=μ-x_n^4$$ as shown below:

Manipulate[Module[{list = NestList[μ - #^4 &, x0, 100]}, list2 = list;
Column[{ListLinePlot[list, PlotRange -> {-1, 1.5},
ImageSize -> {450, 375}],
TableForm[Transpose@{Range[86, 101], list[[-16 ;;]]},
TableHeadings -> {None, {"point", "x"}}]}]], {{μ, 0.2,
"parameter μ"}, 0, 4,
Appearance -> "Labeled"}, {{x0, 0.4,
"Initial \!$$\*SubscriptBox[\(x$$, $$0$$]\)"}, 0, 1,
Appearance -> "Labeled"}]


and one can see the period two cycle (red and green are the points that repeat themselves) for a certain value of $μ$. For a 2D system, in our case the Henon map, period-$2$ cycle means that the system: $$1)x_1=y_2+1-αx_2^2,\quad y_1=β x_2 \\ 2)x_2=y_1+1-αx_1^2, \quad y_2=β x_1$$ has a unique solution and that this solution consists of two pairs of points $(x_1,y_1)$ and $(x_2,y_2)$. In this case the trajectory jumps between these two points on the plane (while at the 1D case it would be on a line).

I am actually curious how one would do it. I mean now, it has to return a pair of points each time right?

Finally, I would like to plot the Henon map after lets say $n=100$ iterations for $β=0.3$ fixed and $α$ varying until $. How can I do that? Thank you all in advance! EDIT Since the Henon Map is defined as above $$x_{n+1}=y_n+1-αx_n^2, \quad y_{n+1}=β x_n$$ all I actually need is to do the same but just for the$x_{n+1}$of the system because (and I just realized this)$y_{n+1}$is just$β$times the$x_n$part! Therefore, I just want to plot$x_{n+1}$vs$n$and then I can deduce the value of$y_n$but definition of the map! I guess that is correct, right? • I removed my answer for the time being. It will have to be up to someone else to find period doubling bifurcations. – C. E. Jun 30 '16 at 11:53 • @C.E. I can still the plot command you helped me with while giving time for someone to help with the period doubling. Could you please post again? – Mitscaype Jun 30 '16 at 12:02 • ok, I've undeleted my answer. – C. E. Jun 30 '16 at 12:15 • You have lumped together a simple mathemaitca question with one that is arguably out of scope of this site. At the very least you should show how you compute the "period" of the sequence. – george2079 Jun 30 '16 at 14:51 • @george2079 Ok, I mistakenly took for granted that the period doubling was something widely known. I will edit the question. – Mitscaype Jun 30 '16 at 14:53 ## 2 Answers Here is the equivalent of your 1-d approach, using @ ce's henon henon[alpha_, beta_][{x_, y_}] := {y + 1 - alpha x^2, beta x} Manipulate[ list = NestWhileList[henon[a, b], {1, 1}, Max[Abs[#]] < 200 &, 1, 2000]; ListPlot[list[[-Min[20, Length@list] ;;]], PlotRange -> All], {{a, -.3}, -1, 1}, {{b, -.4}, -1, 1}]  the trick here is to use NestWhile set up to abort when the sequence diverges. I didn't have any luck finding solutions, but it should get you started. Edit: another approach: (this take a few minutes) err[a_?NumericQ, b_] := StandardDeviation[#[[-Min[20, Length@#] ;;, 1]] &@ NestWhileList[henon[a, b], {1, 1}, Max[Abs[#]] < 200 &, 1, 2000]] s = NMinimize[ err[a, b] , {a, b}]  {0., {a -> -0.329763, b -> -0.485251}}  NestWhileList[henon[a, b] /. s[], {1, 1}, Max[Abs[#]] < 200 &, 1, 20]  {{1, 1}, {2.32976, -0.485251}, {2.30463, -1.13052}, {1.62096, -1.11832}, {0.748128, -0.786571}, {0.397995, -0.36303}, {0.689205, -0.193128}, {0.963511, -0.334437}, {0.971699, -0.467544}, {0.843817, -0.471518}, {0.763282, -0.409463}, {0.782657, -0.370383}, {0.831613, -0.379785}, {0.848273, -0.403541}, {0.833745, -0.411625}, {0.817603, -0.404575}, {0.815862, -0.396743}, {0.822758, -0.395898}, {0.827328, -0.399244}, {0.826469, -0.401462}, {0.823783, -0.401045}} • Thank you for taking time to help me with this one. On the first piece of code that you provided I tried to run it but it returns "aborted" error. I really dont know why this happens :/ The second part of your answer runs perfectly, but to be honest, I do not understand what exactly is it doing. Is it predefining in some way the parameters$α,β$? Because I would like to vary them. I will also edit the question a bit, have a look. Thanks again – Mitscaype Jun 30 '16 at 18:45 • It is ok now, I managed to make it work. I used from your code just to print the$x\$ values and tried to see it as 1D. I find the correct results. Again, many many thanks! – Mitscaype Jun 30 '16 at 20:53

First define the map:

henon[alpha_, beta_][{x_, y_}] := {y + 1 - alpha x^2, beta x}


And then you can do something like

list = NestList[henon[1.4, 0.3], {1, 1}, 10000];
ListPlot[list] It is straightforward to wrap this in Manipulate.

• Thank you for your answer. Does {1,1} inside your code stand for initial conditions? Also, what about the main part of the question? Do you know any possible way that this can be done? Again, thanks! – Mitscaype Jun 30 '16 at 11:33
• Yes, {1,1} is the initial values. I don't know how to find the period doublings at this moment. – C. E. Jun 30 '16 at 12:16
• Is it possible that you also put it in Manipulate? I know it sounds a bit silly, but I am doing something wrong with it. – Mitscaype Jun 30 '16 at 12:39
• @Mitscaype Like this: Manipulate[ ListPlot[NestList[henon[alpha, 0.3], {1, 1}, 1000]], {alpha, 1.3, 1.4}, ContinuousAction -> False] but watch out, it seems like it will overflow if alpha is larger than 1.4, if you do enough iterations. – C. E. Jun 30 '16 at 12:48