# Solve 2 coupled 2nd ODEs and plot them with ParametricPlot?

Posted 11 months ago
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 I am interested to solve two coupled 2nd order differential equations and plot the solution using ParamatricPlot. Can anyone help me to resolve this issue? The solution is a trajectory of a particle under the influence of gravity. So, I am also interested to animate the trajectory of the particle as well. I have attached the Mathematica script with this post. Attachments:
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Posted 11 months ago
 Hi, maybe you can apply the programming concepts from the Trott Springs Example?
Posted 11 months ago
 Thanks for your response. I shall go through the Trott Springs example. However, I have not yet found any mistake in the Mathematica notebook that I attached with the previous post. Do you see any obvious mistake in that script?
Posted 11 months ago
 After correcting a typo (NDSolve) I got an error message NDSolve::derlen: The length of the derivative operator Derivative[2] in (x^\[Prime]\[Prime])[t] is not the same as the number of arguments. 
Posted 11 months ago
 What was the typo ? Do you understand the message you received ?
Posted 11 months ago
 The S was left out of NDSolve. I don't understand the error msg.
Posted 11 months ago
 After correcting works fine: Attachments:
Posted 11 months ago
 Now I have made all the corrections. It is working fine. Thank you once again. Can you please let me know the way to animate the curve ? E.g. a solid circle is moving and as it moves forward a red lines is drawn. Hope I am clear enough.Soumen
Posted 11 months ago
 Attachments:
Posted 11 months ago
 Dear Mariusz, Thank you once again. The animation that you shared in your past post is exactly what I wanted. However, I am unable to reproduce the same using the mathematica notebook ("testplot ver2.nb"). It does not show the black dot and the curve near the point (x=1,y=0) fluctuates. Do you have any idea about the origin of this problem ? Kindly confirm if you have the correct notebook file.Regards Soumen
Posted 11 months ago
 I corrected Mathematica notebook.In Animate function we can't start T from 0, because Mathematica gives error message.Workaround is gives a very small number (10^-15). Attachments:
Posted 11 months ago
 Dear Mariusz Iwaniuk, Thanks for your response. Following your response I have made necessary corrections in my notebook. However, I still find error messages. Can you share your Mathematica notebook file? NDSolve::ndnum: Encountered non-numerical value for a derivative at t == 0.. >> `Regards Soumen
Posted 11 months ago
 Dear Mariusz Iwaniuk, This is just a continuation of my previous post on the trajectory of the particle. The trajectory is not periodic if you run it for long time. In order to make the trajectory periodic up to a good accuracy, I tried to estimate the initial velocity of the particle (i.e. black dot) given the initial position and working precision under consideration. However, I am struggling with FindMinimum function to get the final results. Please help me to find any syntax error in notebook.Regards Soumen Attachments: