The recursive systems of equations with the following form, have they ever been considered?












4












$begingroup$


Suppose a system of 2 equations defined as:



$$begin{cases}
x_{n+1}&=f_x(x_n,y_n) \
y_{n+1}&=f_y(x_n,y_n)
end{cases}$$



where initial conditions for $x_0$ and $y_0$ are defined, and $x_n,y_ninBbb R$, $f_x,f_y:Bbb R^2to Bbb R$.



I found that if $f_x(x,y)=cos(x+y)+sin(x-y)$ and $f_y(x,y)=cos(x-y)+sin(x+y)$. Then the system becomes



$$begin{cases}
x_{n+1}&=cos(x_n+y_n)+sin(x_n-y_n)\
y_{n+1}&=cos(x_n-y_n)+sin(x_n+y_n)
end{cases}$$



which for any starting values for $x_0$ and $y_0$ it will produce the following points(plotted $x$ horizontally and until $x_{1.000.000}$):





which creates a rather interesting structure(I think its called an attractor), and I'd love to hear more about these systems, but couldn't find anything. Any help would be appreciated. Thanks.



EDIT:



If the system is



$$begin{cases}
x_{n+1}&= cos(x_n^2+y_n^2) \
y_{n+1}&= sin(x_n^2-y_n^2)
end{cases}$$



The points would be the following:





Are these coming from some differential equations?










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$endgroup$








  • 1




    $begingroup$
    Maybe using the equation $cos(a+b)=Re(e^{i(a+b)})$ and $sin(a + b) = Im(e^{i(a + b)})$ and combining two levels of the recursion it's possible to find simpler equation for the same system?
    $endgroup$
    – Esa Pulkkinen
    Feb 1 at 20:32
















4












$begingroup$


Suppose a system of 2 equations defined as:



$$begin{cases}
x_{n+1}&=f_x(x_n,y_n) \
y_{n+1}&=f_y(x_n,y_n)
end{cases}$$



where initial conditions for $x_0$ and $y_0$ are defined, and $x_n,y_ninBbb R$, $f_x,f_y:Bbb R^2to Bbb R$.



I found that if $f_x(x,y)=cos(x+y)+sin(x-y)$ and $f_y(x,y)=cos(x-y)+sin(x+y)$. Then the system becomes



$$begin{cases}
x_{n+1}&=cos(x_n+y_n)+sin(x_n-y_n)\
y_{n+1}&=cos(x_n-y_n)+sin(x_n+y_n)
end{cases}$$



which for any starting values for $x_0$ and $y_0$ it will produce the following points(plotted $x$ horizontally and until $x_{1.000.000}$):





which creates a rather interesting structure(I think its called an attractor), and I'd love to hear more about these systems, but couldn't find anything. Any help would be appreciated. Thanks.



EDIT:



If the system is



$$begin{cases}
x_{n+1}&= cos(x_n^2+y_n^2) \
y_{n+1}&= sin(x_n^2-y_n^2)
end{cases}$$



The points would be the following:





Are these coming from some differential equations?










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    Maybe using the equation $cos(a+b)=Re(e^{i(a+b)})$ and $sin(a + b) = Im(e^{i(a + b)})$ and combining two levels of the recursion it's possible to find simpler equation for the same system?
    $endgroup$
    – Esa Pulkkinen
    Feb 1 at 20:32














4












4








4





$begingroup$


Suppose a system of 2 equations defined as:



$$begin{cases}
x_{n+1}&=f_x(x_n,y_n) \
y_{n+1}&=f_y(x_n,y_n)
end{cases}$$



where initial conditions for $x_0$ and $y_0$ are defined, and $x_n,y_ninBbb R$, $f_x,f_y:Bbb R^2to Bbb R$.



I found that if $f_x(x,y)=cos(x+y)+sin(x-y)$ and $f_y(x,y)=cos(x-y)+sin(x+y)$. Then the system becomes



$$begin{cases}
x_{n+1}&=cos(x_n+y_n)+sin(x_n-y_n)\
y_{n+1}&=cos(x_n-y_n)+sin(x_n+y_n)
end{cases}$$



which for any starting values for $x_0$ and $y_0$ it will produce the following points(plotted $x$ horizontally and until $x_{1.000.000}$):





which creates a rather interesting structure(I think its called an attractor), and I'd love to hear more about these systems, but couldn't find anything. Any help would be appreciated. Thanks.



EDIT:



If the system is



$$begin{cases}
x_{n+1}&= cos(x_n^2+y_n^2) \
y_{n+1}&= sin(x_n^2-y_n^2)
end{cases}$$



The points would be the following:





Are these coming from some differential equations?










share|cite|improve this question











$endgroup$




Suppose a system of 2 equations defined as:



$$begin{cases}
x_{n+1}&=f_x(x_n,y_n) \
y_{n+1}&=f_y(x_n,y_n)
end{cases}$$



where initial conditions for $x_0$ and $y_0$ are defined, and $x_n,y_ninBbb R$, $f_x,f_y:Bbb R^2to Bbb R$.



I found that if $f_x(x,y)=cos(x+y)+sin(x-y)$ and $f_y(x,y)=cos(x-y)+sin(x+y)$. Then the system becomes



$$begin{cases}
x_{n+1}&=cos(x_n+y_n)+sin(x_n-y_n)\
y_{n+1}&=cos(x_n-y_n)+sin(x_n+y_n)
end{cases}$$



which for any starting values for $x_0$ and $y_0$ it will produce the following points(plotted $x$ horizontally and until $x_{1.000.000}$):





which creates a rather interesting structure(I think its called an attractor), and I'd love to hear more about these systems, but couldn't find anything. Any help would be appreciated. Thanks.



EDIT:



If the system is



$$begin{cases}
x_{n+1}&= cos(x_n^2+y_n^2) \
y_{n+1}&= sin(x_n^2-y_n^2)
end{cases}$$



The points would be the following:





Are these coming from some differential equations?







recurrence-relations systems-of-equations






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edited Feb 1 at 22:45









flawr

11.8k32546




11.8k32546










asked Feb 1 at 20:14









GarmekainGarmekain

1,502720




1,502720








  • 1




    $begingroup$
    Maybe using the equation $cos(a+b)=Re(e^{i(a+b)})$ and $sin(a + b) = Im(e^{i(a + b)})$ and combining two levels of the recursion it's possible to find simpler equation for the same system?
    $endgroup$
    – Esa Pulkkinen
    Feb 1 at 20:32














  • 1




    $begingroup$
    Maybe using the equation $cos(a+b)=Re(e^{i(a+b)})$ and $sin(a + b) = Im(e^{i(a + b)})$ and combining two levels of the recursion it's possible to find simpler equation for the same system?
    $endgroup$
    – Esa Pulkkinen
    Feb 1 at 20:32








1




1




$begingroup$
Maybe using the equation $cos(a+b)=Re(e^{i(a+b)})$ and $sin(a + b) = Im(e^{i(a + b)})$ and combining two levels of the recursion it's possible to find simpler equation for the same system?
$endgroup$
– Esa Pulkkinen
Feb 1 at 20:32




$begingroup$
Maybe using the equation $cos(a+b)=Re(e^{i(a+b)})$ and $sin(a + b) = Im(e^{i(a + b)})$ and combining two levels of the recursion it's possible to find simpler equation for the same system?
$endgroup$
– Esa Pulkkinen
Feb 1 at 20:32










1 Answer
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$begingroup$

Yes, such recurrences have been studied extensively and are still subject to resear in the field of Dynamical Systems, discrete time dynamical systems in particular. In this field the behaviour of repeated applications of a function (in your case $mathbb R^2 to mathbb R^2$) to some inputs is studied.






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    $begingroup$

    Yes, such recurrences have been studied extensively and are still subject to resear in the field of Dynamical Systems, discrete time dynamical systems in particular. In this field the behaviour of repeated applications of a function (in your case $mathbb R^2 to mathbb R^2$) to some inputs is studied.






    share|cite|improve this answer









    $endgroup$


















      1












      $begingroup$

      Yes, such recurrences have been studied extensively and are still subject to resear in the field of Dynamical Systems, discrete time dynamical systems in particular. In this field the behaviour of repeated applications of a function (in your case $mathbb R^2 to mathbb R^2$) to some inputs is studied.






      share|cite|improve this answer









      $endgroup$
















        1












        1








        1





        $begingroup$

        Yes, such recurrences have been studied extensively and are still subject to resear in the field of Dynamical Systems, discrete time dynamical systems in particular. In this field the behaviour of repeated applications of a function (in your case $mathbb R^2 to mathbb R^2$) to some inputs is studied.






        share|cite|improve this answer









        $endgroup$



        Yes, such recurrences have been studied extensively and are still subject to resear in the field of Dynamical Systems, discrete time dynamical systems in particular. In this field the behaviour of repeated applications of a function (in your case $mathbb R^2 to mathbb R^2$) to some inputs is studied.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Feb 1 at 22:35









        flawrflawr

        11.8k32546




        11.8k32546






























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