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Folding an ellipse

By: Matthen on Nov 27th, 2012  |  syntax: None  |  size: 1.43 KB  |  hits: 208  |  expires: Never
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  1. p = RandomReal[{0.2, 0.9}] (({Sin[#], Cos[#]} &)[RandomReal[]]);
  2. R = RotationMatrix[Pi/2];
  3. n = 33;
  4. p2s = Table[{Sin[\[Theta]], Cos[\[Theta]]}, {\[Theta], 0, 2 Pi,
  5.     2 Pi/n}];
  6. ns = Table[R.(p1 - p)/Norm[p1 - p], {p1, p2s}];
  7. frame[i_] := Block[{p1, n1, m, n2},
  8.    n1 = ns[[Mod[i, n, 1]]];
  9.    p1 = p2s[[Mod[i, n, 1]]];
  10.    n2 = (p - p1)/Norm[p - p1];
  11.    n1 = n1/Norm[n1];
  12.    m = (p1 + p)/2;
  13.    Graphics[
  14.     {
  15.      {
  16.       Thick,
  17.       RGBColor[0.1, 0.1, 0.3],
  18.       Circle[{0, 0}, 1]
  19.       },
  20.      If[i > n,
  21.       If[i > 2 n,
  22.        Table[
  23.         Block[{pt, nt},
  24.          pt = p2s[[j]]; nt = ns[[j]];
  25.          {
  26.           Line[{(pt + p)/2 + 10 nt, (pt + p)/2 - 10 nt}]
  27.           }
  28.          ]
  29.         , {j, i - 2 n, n}]
  30.        ,
  31.        Table[
  32.         Block[{pt, nt},
  33.          pt = p2s[[j]]; nt = ns[[j]];
  34.          {
  35.           Line[{(pt + p)/2 + 10 nt, (pt + p)/2 - 10 nt}]
  36.           }
  37.          ]
  38.         , {j, i - n}]
  39.        ]
  40.       ,
  41.       {}
  42.       ],
  43.      Thick,
  44.      PointSize[Large],
  45.      Point[p1],
  46.      Point[p],
  47.      RGBColor[0.3, 0.1, 0.1],
  48.      Line[{p1, p}],
  49.      RGBColor[0.5, 0.1, 0.07],
  50.      Line[{m + 10 n1, m - 10 n1}],
  51.      FaceForm[],
  52.      EdgeForm[Black],
  53.      Polygon[{
  54.        m + 0.1 n2 + 0.1 n1,
  55.        m - 0.1 n2 + 0.1 n1,
  56.        m - 0.1 n2 - 0.1 n1,
  57.        m + 0.1 n2 - 0.1 n1
  58.        }]
  59.      }
  60.     , ImageSize -> 300, PlotRange -> 1.5]
  61.    ];
  62. Manipulate[
  63.  frame[i]
  64.  , {i, 1, 3 n, 1}]
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