How to plot an unstable attractor?
To visualize a 2D system, I would start with StreamPlot
:
vf = {x', y'} /. First@Solve[eqns /. f_[t] :> f, {x', y'}]; (* strip the args *)
StreamPlot[vf, {x, -2, 2}, {y, -2, 2}]
You can use StreamPoints
to highlight the structure and Epilog
to mark the attractor at $(1,0)$:
ics = {{{Cos[1/5], Sin[1/5]}, Red},
{{0.5, 0}, Magenta}, {{1.5, 0.}, Magenta}};
StreamPlot[vf, {x, -2, 2}, {y, -2, 2},
StreamPoints -> {Append[ics, Automatic]},
Epilog -> {White, EdgeForm[Black], Disk[{1, 0}, 0.03]}]
eqns = {x'[t] ==
x[t] - y[t] -
x[t] (x[t]^2 + y[t]^2) + (x[t] y[t])/Sqrt[x[t]^2 + y[t]^2],
y'[t] ==
x[t] + y[t] - y[t] (x[t]^2 + y[t]^2) -
x[t]^2/Sqrt[x[t]^2 + y[t]^2]};
sol = NDSolve[Join[{x[0]==1.5, y[0]==1.5}, eqns], {x, y}, {t, 0, 50}];
ParametricPlot[{x[t], y[t]}/.sol//Evaluate, {t, 0, 50}, PlotRange->All]