Tagged Questions

Questions on the symbolic (DSolve, DifferentialRoot) and numerical (NDSolve) solutions of differential equations in Mathematica.

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Setting Initial Conditions in a System of Differential Equations that don't start at t=0

I have a system of six differential equations (linear for the sake of the discussion). I want to set the initial condition to start at time t=18 and not time t=0. I know the values of the dependent ...
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Solving Time-Dependent PDE's Analytically with no non-trivial Boundary Conditions

I'm having some trouble solving a partial differential equation that is supposed to model the propagation of a scalar field in Schwarzschild spacetime using spherical coordinates. I'm using the DSolve ...
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EventLocator in NDSolve seemingly hogs memory in Windows, but not Mac

I have written a function (ftest in my code) which does the following: Takes a vector {x,vx,vy} as input Numerically solves (with high precision) a specific ...
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NDEigensystem returns incorrect eigenvalues for 2D coulomb problem, eigenfunctions contain discontinuity

I posted a similar question a short time ago regarding the 3D Coulomb problem. Jens' excellent answer to this thread allowed me to obtain the correct eigenvalues and eigenenergies for that system. I ...
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Issues with modeling pulses in a very simple system of DAEs

Bug introduced in 10.4.1 or earlier Bug has been confirmed by WRI [Case:3594387]: It does appear that the NDSolve function is not behaving properly in this case and an incident report has been ...
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How to perform this nth derivative operation in MMA?

I have to solve this following equation where I need to differentiate a function $n$ times. $$A=\sum_{n=0}^{m-1}\frac{s^n}{n!}(-1)^n\frac{d^nf(s)}{ds^n}$$ How to express the above equation in ...
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Recycle boundary condition

I'm having the following issue that can not find a solution , by using this boundary condition u[0, t] == 2 u[1, t] that Mathematica does not understand, someone ...
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Solving ode which solution oscillate violently

This is a ordinary differential equation: y[x]/(-1 + x^4)^2 - ((1 + 2 x^2 + 3 x^4 - 2 x^6) Derivative[1][y][x])/(x - x^5) + Derivative[2][y][x] == 0 I want to ...
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Jump boundary conditions

I'm having the following issue that can not find a solution , by using this boundary condition ...
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How to “INJECT” with holding Evaluation, specifically into a WhenEvent

I am importing a set of differential and stochastic equations from an external package, and want to use Mathematica to analyse this. I am struggling building the set of equations that I can use with <...
41 views

Pass List / Vector argument through NDSolve to a function

I am trying to pass vector or list as argument to the function from NDsolve.And I am getting these error. Also I am pretty new to stack overflow. Apology if this a possible duplicate. Here is my code. ...
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portions of plot missing for a relatively simple function

I am trying to produce a graph of the linear dynamic system response to a step input. The code is as follows: ...
88 views

Free-fall air resistance problem

I´m working on a free fall problem and I got an equation with variable $k$ when the situation has air resistance. Then I compared with no air resistance equation ($-4.9$, considering t variable). So, ...
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How can I identify which solution triggered the WhenEvent?

I am using NDSolve for problems like this: ...
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solving system of ODEs in Mathematica

I am using the DSolve to solve the following 2 ODEs \begin{cases} &\dot{y}(t)=z(t)-y(t)-\frac{c_1c_2y(t)}{-c_1c_2e^{-t}t+c_1(1-c_2)+c_3e^{-t}}\\ &\dot{z}(t)=-z(t)+\frac{...
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Dsolve svars error: Equations may not give solutions for all “solve” variables

New to Mathematica, trying to solve a set of coupled differential equations related to a geodesics/Calculus of Variations problem. More specifically, I am trying to solve the two Euler-Lagrange ...