# Tagged Questions

Questions about approaches for simulating physical systems or phenomena by building from related understanding and basic principles.

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### Mathematica Implementations of the Random Forest algorithm

Is anyone aware of Mathematica use/implementation of Random Forest algorithm?
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### How to perturb a Dynamic System?

I'm trying to model a basic feedback system with delayed feedback. I've done the initial setup and now want to add a few more advanced features to my system. Currently, it's just a simple delayed-...
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### What's the analogue of UML in Mathematica land?

What's the analogue of Unified Modeling Language (UML) in Mathematica land? Mathematica has elements of object-orientation, but most Mathematica programs or applications aren't of object-oriented ...
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### How to do System dynamics simulations / diagrams in Mathematica?

System dynamics is an approach to understanding the behaviour of complex systems over time. It deals with internal feedback loops and time delays that affect the behaviour of the entire system. What ...
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### Mathematica Package for Bayesian Networks

Are there any packages that allow the simulation of Bayesian Networks with Mathematica? I found what seemed to be a promising package (Dynamics) on a Brown University URL, http://www.cs.brown.edu/...
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### Sinusoid modelling

There are lots of great demonstrations that show how to get periodic functions in the unit circle. I'm wondering how hard it would be to simulate a "moving grid" similar to this video on youtube (...
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### Modelling the effect of a structure on a “tsunami” (hyperbolic wave equation)

So, the hyperbolic wave equation can be quite easily solved in Mathematica like this: ...
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### How does Mma compute Confidence Intervals?

I am trying to understand how Mma computes the Confidence Intervals after a NonlinearModelFit. Consider the following example: ...
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### Find fit of an experimental PDF

After quite some struggle, I managed to put up a code that is syntaxically correct. The goal is to find the parameters for a gamma distribution that best match experimental data. The data is a set of ...
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### Computing launch parameters for hitting a point in 3D with projectile under influence of wind

The end goal of this problem is to compute functions which describe the launch parameters which are needed to hit a specified goal in 3D in the presence of wind disturbances. This is as far I have ...
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### Modelling a Rocket Launch using NDSolve

I'm trying to model a rocket launch with Mathematica but I've run into a little problem since I don't know how to turn the thrust off. I'm using Newton's Law of Universal Gravitation plus an added ...
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### Modelling Hysteresis with a Differential Equation

I want to implement the bulk ferromagnetic hysteresis model (mostly the Jiles-Atherton Model), see http://drum.lib.umd.edu/bitstream/1903/6043/1/PhD_99-1.pdf page 44 equation (30). The needed ...
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### RSquared: LinearModelFit vs NonlinearModelFit

I'm trying to understand the differences between LinearModelFit and NonlinearModelFit. One thing I notice is that the ...
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### Sensitivity Analysis: Global Sensitivity and Screening

I have a model which accepts several input parameters and now I want to study the sensitivity to certain parameters as described in here: Cross Validated Answer and in Wikipedia. There is also a link ...
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### Sound synthesizer using Manipulate

Sound synthesizers, both digital and analog, often include a parameter section for shaping the amplitude of a sound wave over time. This parameter section is commonly known as an "ADSR EG" (attack, ...
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### ToDiscreteTimeModel fails following video

Following the systems-modeling video here at about 15 min, 20 seconds in, the presenter (Bob Sanhedrick, I think) shows a model for an "Asteroids-game"-like 2D spacecraft. The model is trivial: <...
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### Plot two functions within manipulate

I just want to plot all stochastic processes and their average process. The original code without the average is: ...
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### How to model Macroeconomic dynamics?

I am rather new to Mathematica and I wanted to see if I could get some help with the following. I am trying to generate a model of macroeconomic indicators defined by the following functions, but I ...
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### Approximate minimum degree permutation algorithm in Mathematica

In MATLAB there is a nice implementation of the so called AMD (approximate minimum degree permutation) algorithm named amd (see Online MATLAB Documentation). There is an alternative algorithm called ...
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### Problem with WhenEvent

I am trying to add a time dependent fraction to a parameter in NDSolve, i.e. when 10 < t< 20, add ...
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### FindFit and NMinimize to fit a parametric model (minimize the distance of two curves)

I am trying to find a fit to the cumulative distribution of a set of points using FindFit or NMinimize. In particular, I would like to find the parameters of the cdf of the Beta Distribution that ...
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### How do I represent a system dynamics feedback loop?

In System Dynamics, if I want represent the relationship between Speed and Distances, I create a Flow (Speed) and a Stock (Distance) as you can see in this Insight Maker Sample . Heres an Image of how ...
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### Problem exporting and re-importing STL file

I wrote all code and there're no errors in code. Result of code is like first picture(left). But I can't Import that structure. The result of import stl file is second one(right one). How can I import ...
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### Second-Order Feedback Pathways [closed]

I'm relatively new to Mathematica and I've tried searching and reading through the Mathematica documentation but I'm not able to find a good place to start. I want to model a simple, second-order ...
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### Plot Plane to Intersect 3D Contour Plot in Mathematica

I have a 3D model of a heart in Mathematica and I'm trying to create a plane so that the open surface (as seen in the image below) is cut off so that the heart can have a solid, level surface. How ...
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### Comparison between numerical solution of nonlinear ode and nonlinear ode of second order

Background Let's consider the following initial value problem for nonlinear system $$\begin{cases} E' &=& 1 - n_e, \\ n_e' &=& -8\,n_e\,E, \end{cases} \tag{1}$$ with the following ...
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### How to combine objects from different .obj files?

I got a screw .obj model with the head diameter of 2cm, and a board .obj model of 10cmx10cmx4cm in dimension. I would like the ...
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### Problem with SARIMA Time Series Model

I'm in the process of becoming familiar with some on the version 10 new functionality. I have two data sets, datasetA and datasetC, of time series data that I would like to make forecasts on. Here is ...
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### ParametricNDSolve and Constraint satisfaction problem

I am trying to find the values of two parameters that allow for a specific result of my differential equations, under different initial conditions. Given a system of equations: ...
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### Generating a “best fit” curve to a set of noisy data corresponding to a moving object

Please note that this is an extension of a previous question: Interpolating a sparse list of two-dimensional coordinates We have an ordered array of coordinates corresponding to the position of an ...
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### How to do multi-agent modeling?

There are tons of examples here: http://demonstrations.wolfram.com/topic.html?topic=multi-agent+modeling&limit=20 But I been unable to find a good guide explaining what is the recommended ...
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### Model fitting to noisy data with a custom minimization function

I'm looking into fitting some data with Mathematica. I've got my head around how NonlinearModelFit works (I've been using the Levenberg-Marquardt algorithm for some ...
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### Extract Transfer Matrix from TransferFunctionModel

I have a MIMO transfer function model, and I'd like to know how to perform arithmetic on this model. For instance, to see the difference between two systems' outputs for arbitrary inputs, I'd like to ...
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### How can I calculate the maximum number of grid layout possibilities?

I am doing some modelling where I am trying to randomly layout some points on a grid. What I know: How big the grid is The number of objects that have to be laid out on the grid, at a point The ...
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### PlotRange problems

I have a Delay Differential Equation of the form: ...
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### How can I model the volatility, using a GARCH(1,1), of a time series of returns (and plot it) using Mathematica?

I know that if I use this code: tsm = TimeSeriesModelFit[ret, {"GARCH", {1, 1}}]; I can get the parameters using this: ...
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### Determining the total illumination of a polygon

Is it possible to determine the total illumination of a particular polygon with the given light sources? I truly acknowledge that Mathematica is not supposed to do this modeling, but it is what is ...
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### How to use a random number generator as an independent variable in an existing model?

I am relatively new to Mathematica and I need some help regarding how to create a random number generator to be used as an independent variable for a model my group has been working on. Following is ...
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### Fitting a Damped Sine to Data

I have some collected data that should be modeled by a damped oscillation. Here are the data in a list of ordered pairs: ...
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### How to simulate Multifractional Brownian Motion?

The maximum I would ask, is hints, how to model MFBMotion. Link to paper Firstly, i wanted to simulate in MATLAB that code: ...
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### Modeling a stellar atmosphere

I'm trying to model a stellar atmosphere using Mathematica. Basically I'm working in a physical and chemical model which combined should give me a profile of the chemical abundance in the atmosphere. ...
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### Animating a 3D shape along path a (2D and 3D) parametric function curve [Update]

I have a 3D object under the action of gravity field.The trajectory of path is a parabola.I would like to animate , as in the example GIF. ...
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### Multivariable non-linear fitting

I have a function called "C" that I know it depends on 6 variable. I have a set of data points, 6 rows by 9 columns, in which in each row only one variable is changing and the rest of the variables ...
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### How to make this model in wolfram mathematica?

A model production possibility curve (nonlinear case). I used 1/4 of a circle in the code. ...
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### Phase Portrait to Differential Equation [closed]

I posted this question on Math.SE and have received a satisfactory answer in the context of that website. I am re-posting it here to get input from Mathematica users. Why would I receive a different ...
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### Generate a simulated covariance matrix

I am working on a problem where one of the input variables is the level of covariance between the entries in a particular matrix. To simulate this problem in Mathematica, I will need to feed my code ...
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### Transposition of state space form of a transfer function

How can I transpose the output of state space model in Mathematica? trying the following code would transpose the top right symbol s instead of the matrices. ...
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### Creating an animated graph model based on equations

So I have a graph that looks like this ...