# Questions tagged [nonlinear]

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

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### Transform a set of nonlinear equations in state space form

I have to solve a multi-body dynamic problem numerically in Matlab. The set of equations has been computed in Mathematica. To solve it in Matlab i have to transform it into state space representation. ...
• 11
76 views

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### NonlinearModelFit of data with errors

Experimental data points invariably come with errors. These errors can significantly influence the parameters and their uncertainties when performing non-linear fitting. However, NonlinearModelFit ...
• 3,491
146 views

### Fitting data with ${\rm sinc}^2(x)$

I performed an experiment of Fraunhofer diffraction with slits, the results of which should be proportional to $\operatorname{sinc}^2(x) = \left(\frac{\sin x}{x}\right)^2$. However, an error occurred ...
1 vote
90 views

### Problem to solve computationaly and plot the phase portrait of a nonlinear ode system

I am here again to see if some one can help me. This time, I have problem to solve, computationally and plot the phase portrait of a nonlinear ode system (The Duffing Equation with just the spring ...
83 views

### Time independent perturbation theory for solving coupled differential equations

The eqexact1 and eqexact2 are the coupled differential equation of motion with g lets say a repulsive factor, that I choose. ...
1 vote
94 views

### Simultaneous NonlinearModelFit for two data sets that are separate functions of x and t [duplicate]

I am trying to simultaneously fit two data sets that are separate functions of $x$ and $t$ with NonlinearModelFit. Here is an example of the data: ...
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### Solving differential equation with hyperbolic functions

I've been trying to solve the following differential equation: \left( \frac{d \tau}{d \sigma} \right)^2 = \frac{(E_0 \cosh\sigma-p_\tau\sinh\sigma)^2}{(E_0 \cosh\sigma-p_\tau\sinh\...
1 vote
78 views

### Fitting linear decay to a semilogarithmic line

I am trying to fit this set of data,I tried a simple linear model but it didn't yield successful results, I also tried curve_fit on Python but also no luck - here ...
93 views

### Set of differential equations with trigonometric functions and a derivative squared

I've been trying to solve a set of differential equations that involve the square of a derivative, similar to another post I made here, and trigonometric functions, as seen here \frac{...
463 views

### Solving coupled differential equations involving the square of the derivative

I want to solve the following system of coupled differential equations in order to obtain particle trajectories: $$\frac{dt}{ds} = (E-y\, p_t)y$$ \...
1 vote
133 views

### Nonlinear experimental data fit without initial parameters

I am trying to fit correlation data into a non-linear model but it is not working. My data plot looks like this: The equation I am using for fit is The Mathematica script i am using looks like: <...
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1 vote