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# Compare the symbolic solution with numerical solution

Posted 1 year ago
 I am trying to compare the symbolic solution with numerical solution by using NDSolve. But the two curves are not match when I plot it. Please give me suggestions how to improve the plot?
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Posted 1 year ago
 You give initial data that do not match xIII: {xIII[0], xIII'[0], xIII''[0]} With[{ww = 10^(-2), tt = 1}, {x0 = xA /. w -> ww, x0p = Sqrt[ww - x0^2 - (1/4) x0^4], x00p = -x0 - (1/2) x0^3}] // N How can you expect the solutions to coincide?
Posted 1 year ago
 num = NDSolveValue[ eq1 && (x[0] == xIII[0]) && (x'[0] == xIII'[0]) && (x''[0] == xIII''[0]), x, {t, -1, 1}]; ReImPlot[num[t] - xIII[t], {t, -1, 1}] 
Posted 1 year ago
 xIII[t_] = 2 I Sec[t]; 
Posted 1 year ago
 I tried it, but no plot output on my computer.
Posted 1 year ago
 Gianluca's answer works fine for me. You probably have a conflicting prior definition for some symbol(s). Try with a fresh kernel or evaluate the following prior to evaluating the rest of the code. ClearAll[Evaluate[Context[] <> "*"]] 
Posted 1 year ago
 still no output plot. I got just one result i.e., Attachments:
Posted 1 year ago
 I don't understand. The function xIII does not seem to be a solution of eq1: Simplify[eq1 /. x -> xIII] 
Posted 1 year ago
 Sorry "xIII=2 i sec(t)", then output is true.
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