[GIF] Trifolium (Envelope of the trifolium curve)

lem8.gif

Trifolium

The animation shows 800 tangent lines to the trifolium as they slowly move around the curve. In order to make it, I first ran PlaneCurveData["Trifolium", "ParametricEquations"] to get the parametrization, which I then rotate to get a vertically-oriented trifolium:

tri[t_] := RotationMatrix[?/6].{-Cos[t] Cos[3 t], -Cos[3 t] Sin[t]};

After that, it’s just a matter of creating the tangent lines with InfiniteLine[] and choosing some colors. Here’s the code:

With[{d = 2 ?/800.},
 Manipulate[
  Show[
   Table[
    Graphics[{Thickness[.001], Opacity[.8], Hue[Mod[(s + t)/?, 1]],
      InfiniteLine[tri[t + s], tri'[t + s]]},
     PlotRange -> {{-1.4, 1.4}, {-1.18125`, 1.61875`}}],
    {t, 0., ? - d, d}],
   ImageSize -> 540, Background -> GrayLevel[.1]],
  {s, 0, d}]
 ]
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