I have a somewhat convoluted problem and am not a Mathematica expert. I am trying to solve (numerically) the Euler-Lagrange equations for a complex Lagrangian. The difficulty lies in the fact that L(x(t), xdot(t), t) depends on the integral over a region that itself depends on x(t).
The issue is that when I supply the Euler-Lagrange equations to Mathematica, it tries to evaluate the ImplicitRegion before solving, which of course fails as the region depends on x(t).
Is there a way to formulate this problem so that Mathematica evaluates the region and integral dynamically? Defining the region analytically based on x(t) and defining the integral explicitly is not an option due to the dynamic complexity of the region.
Added detail:
Here's the Lagrangian:
L[q_, t_] := Module[{ R, S, \[ScriptCapitalR], \[ScriptCapitalS]},
R = ((outerL2[q, t][[1]] <= x <= innerL2[q, t][[1]]) && (y <=
outerL1[q, t][[2]])) || ((innerL1[q, t][[2]] <= y <=
outerL1[q, t][[2]]) && (x >= innerL2[q, t][[1]]));
S = ((-1 <= x <= 0) && (-3 <= y <= 1));
\[ScriptCapitalR] = ImplicitRegion[R, {{x, -3, 3}, {y, -3, 3}}];
\[ScriptCapitalS] = ImplicitRegion[S, {{x, -3, 3}, {y, -3, 3}}];
Return[4 -
NIntegrate[
1, {x, y} \[Element]
RegionIntersection[\[ScriptCapitalR], \[ScriptCapitalS]]]]
]
NDSolve, but for some cases, the problem can be solved with a little extra programming (often much simpler than in other languages!); and in some cases, the equation can be transformed to eliminate the integral term. Anyway, click the [tag:integral-equations] tag and you'll see existing examples, these might help. – xzczd Feb 17 '24 at 10:29_?NumericQ? See this post for more info: https://mathematica.stackexchange.com/a/26037/1871 – xzczd Feb 17 '24 at 11:07