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NDSolve for a system of second order differential equations

Posted 11 days ago
5 Replies
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Hello everyone :) I'm new in using Mathematica, so I hope the script is clear! I'm trying to solve this system of two second order differential equations; they are linked by the boundary conditions (it's a physic model and it should be correct). When I evaluate the solution, this warning happens: "NDSolve:Equation or list of equations expected instead of True in the first \ argument". I checked if there are some mistakes in the script, but it should be correct. Could anyone help me by checking for some mistakes or improving the script?

5 Replies
Posted 11 days ago

Hi Lorenzo,

The code in the attached notebook uses DSolve, the error you reported is from NDSolve. Did you attach the right notebook? The error message I get is

DSolve::deqx: Supplied equations are not differential or integral equations of the given functions.

DSolve[eqns, {x, y}, t]

The equations in eqns do not depend on x, y, or t. Need to use the functions and independent variables in eqns as the arguments to DSolve

Hi Rohit, thanks for the answer! Yes, I attached by mistake the wrong file. This is the correct one. Hope you can help me now! :)


This is the updated file, still I have some problems:

Posted 10 days ago


The first equation in eqns has Sqrt[1 + 0.2304*Subscript[ξ, 1]^2]. There is no definition for Subscript[ξ, 1]. There may be other issues as well.

Thanks! Still I have this warning: "NDSolve::ndnum: Encountered non-numerical value for a derivative at [Xi] == -1.." . Do you know if there is something wrong with some definitions I made, or something that tells to the NDSolve command to evaluate the equations for all the [Xi] except [Xi]=-1?

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