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Matthen

Evolute

Nov 21st, 2012
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  1. x[t_] := (1 + Cos[t]) Sin[t];
  2. y[t_] := -(1 + Cos[t]) Cos[t];
  3. tmin = 0; tmax = 2 Pi;
  4. n = 41;
  5. notzero[x_] := If[x == 0, 0.001, x];
  6. normals = N@Table[{y'[t], -x'[t]}, {t, tmin, tmax, (tmax - tmin)/n}];
  7. ps = N@Table[{x[t], y[t]}, {t, tmin, tmax, (tmax - tmin)/n}];
  8. ts = N@Table[t, {t, tmin, tmax, (tmax - tmin)/n}];
  9. X[t_] := x[t] -
  10. y'[t] ( x'[t]^2 + y'[t]^2)/notzero[x'[t] y''[t] - x''[t] y'[t]];
  11. Y[t_] := y[t] +
  12. x'[t] ( x'[t]^2 + y'[t]^2)/notzero[x'[t] y''[t] - x''[t] y'[t]];
  13. Manipulate[
  14. Show[
  15. Graphics[{}, PlotRange -> {{-2, 2}, {-3, 1}},
  16. ImageSize -> {300, 300}],
  17. Reverse@Table[
  18. ParametricPlot[
  19. ps[[i]] + t normals[[i]]/notzero@Norm[normals[[i]]], {t, -100,
  20. 100},
  21. PlotStyle ->
  22. If[i == \[Tau] || i == \[Tau] - Length@ts,
  23. Directive[Thickness[0.01], RGBColor[0.4, 0.4, 0.9]],
  24. Directive[Thick, Opacity[0.4], RGBColor[0.1, 0.1, 0.1]]]
  25. ], {i, If[\[Tau] > Length[ts], \[Tau] - Length[ts], 1],
  26. If[\[Tau] > Length[ts], Length[ts], \[Tau]]}],
  27. ParametricPlot[{{x[t], y[t]}, {X[t], Y[t]}}, {t, tmin, tmax},
  28. PlotStyle -> {Directive[Thick, RGBColor[0.9, 0.2, 0.3]],
  29. Directive[Thick, RGBColor[1.0, 0.1, 0.2]]}],
  30. Graphics[{PointSize[0.05], RGBColor[0.2, 0.2, 0.6],
  31. Point[ps[[Mod[\[Tau], Length@ts, 1]]]]}]
  32. ],
  33.  
  34. {\[Tau], 1, 2 Length[ts], 1}]
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