NDSolve for a system of second order differential equations

Questions
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1

Hello everyone :slight_smile: 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?

SpostamentoTrave6.nb (22.6 KB)

2

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

3

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! :slight_smile:

SpostamentoTrave6.nb (22.6 KB)

4

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

SpostamentoTrave7.nb (26.5 KB)

5

Lorenzo,

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.

6

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?