# How to export an animation for a numerically solved system

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 Lucas Morales 2 Votes I've been trying to put together a double pendulum animation for my physics project. forces = {m1*       x1''[t] == (\[Lambda]1[t]/l1) x1[t] - (\[Lambda]2[t]/        l2) (x2[t] - x1[t]),     m1* y1''[t] == (\[Lambda]1[t]/l1) y1[t] - (\[Lambda]2[t]/        l2) (y2[t] - y1[t]) - m1* g,     m2* x2''[t] == (\[Lambda]2[t]/l2) (x2[t] - x1[t]),     m2* y2''[t] == (\[Lambda]2[t]/l2) (y2[t] - y1[t]) - m2* g}; constraints = {x1[t]^2 + y1[t]^2 ==      l1^2, (x2[t] - x1[t])^2 + (y2[t] - y1[t])^2 == l2^2};initialconditions = {x1[0] == 1, y1[0] == 0, x1'[0] == 0, y1'[0] == 0,   x2[0] == 1, y2[0] == -.6, x2'[0] == 0,   y2'[0] == 0}; constants = {g -> 9.8, m1 -> 1, m2 -> 1, l1 -> 1,   l2 -> .6}; solution = First[NDSolve[{forces, constraints, initialconditions} /.     constants, {x1, y1, x2, y2, \[Lambda]1, \[Lambda]2}, {t, 0, 100},    Method -> {"IndexReduction" -> {"Pantelides",        "ConstraintMethod" -> "Projection"}}]]; Animate[ Graphics[{{PointSize[.025], {Gray, Point[{x1[t], y1[t]}]}, {Orange,       Point[{x2[t], y2[t]}]},      Line[{{0, 0}, {x1[t], y1[t]}, {x2[t], y2[t]}}]} /.     solution, {Orange,     Line[Map[Function[Evaluate[{x2[#], y2[#]} /. solution]],       Range[0, t, .025]]]}, {Gray, Opacity[.5],     Line[Map[Function[Evaluate[{x1[#], y1[#]} /. solution]],       Range[0, t, .025]]]}}, PlotRange -> {{-1.6, 1.6}, {-1.8, 0}},   Axes -> False, Ticks -> False, ImageSize -> 500], {{t, , "Time"}, 0,   7, .0000001}, DefaultDuration -> 40, RefreshRate -> 30]I've been trying to export this usingĀ Export["m.avi",%]But the result I get is a 4 second long video that looks like this the entire timeĀ The output Mathematica gives after the animate command is the kind of thing i'm looking for -- a 40 second video of the double pendulum starting from the initial conditions of rest. Am I doing anything wrong?
4 years ago
6 Replies
 Frank Kampas 1 Vote I generated an animated GIF in code that is here: Animating Optimization with the Gradient Projection Method
4 years ago
 Frank, you can easily upload animated GIFs to the community - as we did for your post. It is done in the same way you upload a regular image. To read how please refer to: How to type up a post: editor tutorial & general tips
4 years ago
 Sam Carrettie 3 Votes Lucas, it is a beautiful animation, but there is a typo in your posted code that causes the problem - as you can see on the image below you did not specify initial moment of time - it should be zero between those 2 comas. On a general note, the movie you export will be too fast. For precision control I suggest using Table, not animate and control the number of frames - table values - the more frames you have the slower is the movie. Basically this you need this approach, just change GIF to AVI: How to export GIFs