# Questions tagged [nonlinear]

Used to mark questions about nonlinear differential equations, NonlinearModelFit, and related to nonlinear dynamics.

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### NDSolve:Coupled PDE's, initial-boundary value problem: unreasonable "insufficient number of boundary conditions" error

I tried to NDSolve the PDE system: $$\partial_t y = x\partial_z w \quad\quad \partial_t w = \partial_z y \quad \quad \partial_z x=w$$ for $$(t,z)\in[0,1]\times[-1,0]$$ with initial conditions x(...
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### Linearization of ODE without an equilibrium

Given: $\begin{cases} \dot{x}=-x^2+\frac{1}{y+1}+1 \\ \dot{y}=1 \end{cases}$ I am trying to linearize the system in the classical way, using the Jacobi matrix. ...
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### Need help solving a system of two 1st order nonlinear differential equations

The original system of equations reads: $\begin{cases} f'(r) + f(r) \left(a(r) - \frac{1}{r}\right) = 0,\\ f^2(r) + a'(r) + \frac{a(r)}{r} - 1 = 0\,, \end{cases}$ with boundary conditions \$f(0) = 0\,...