# Tag Info

Accepted

### In what way can M11.3's system modelling features be used by those who don't have SystemModeler?

I'm one of the developers behind this functionality, so I might be biased, but in my opinion this does provide a huge new feature set to Mathematica users. What practical use do these new functions ...
• 2,442
Accepted

### Backtesting a Probability of Default (PD) model

This kind of backtest is often performed using approximations, for instance with normal distributions, which may not be always valid. An exact test would be very nice to have. The probability ...
• 64.6k

### My Girlfriend is going to prison...Save her with Math

Similar to previous answers, only I don't make the instantaneous absorption assumption since it isn't really necessary. The equation can be found here on page three, where ka and ke are the rates of ...
• 19.4k
Accepted

### Couple a PDE and ODE in NDSolve

Modified Newton Cooling Law implementation and reduced FEA cell length ...
• 7,247
Accepted

### Sound synthesizer using Manipulate

First let me observe that your coding style makes debugging difficult, I highly recommend breaking giant expressions into manageable pieces. Second, in the code below I have used a different ...
• 83.6k

### Generating random sequence of integers with ordering constraints

Perhaps have a look at DiscreteMarkovProcess using an appropriate transition matrix embedding your constraints? Here's a simple example, implementing 1-5 above, to ...
• 3,995

### My Girlfriend is going to prison...Save her with Math

Assuming the simplest kinetic model for elimination (and making the simplifying assumption of "instant absorption" to peak concentration): ...
• 55.2k

### Mass Transport Model

OK. Let me extend my comments to an answer. First of all, I'd like to point out why OP's attempt doesn't work: "NDSolveValue should return a list with three ...
• 54.2k
Accepted

### My model has not finished evaluating in more than a day so can't test if it works, what is wrong with it?

Here a couple of changes/suggestions. Using a decimal dot for all constants forces most algorithms to switch from symbolic to numeric routines with machine floating point arithmetic; that's typically ...
• 96.4k
Accepted

### Why does NonlinearStateSpaceModel linearise?

Consider a model where the nonlinearity is in $x'(t)$ and not in the highest derivative $x''(t)$. eq1 = {x''[t] + Sin[ x'[t]] + x[t] == u[t]}; Choose the first ...
• 8,382
Accepted

### Can I use a differential equation as a model to make a fit to experimental data?

Mimicking the examples in FindFit >> Applications >> DifferentialEquations NonlinearModelFit >> Generalizations and Extensions ...
• 350k
Accepted

### Speed up NDSolve compared to Python (calls to LSODA)

First question. I'm pretty sure that the difference is due to what happens with machine underflow. As of V11.3, underflow goes to machine zero instead of to arbitrary-precision numbers (as it does in ...
• 220k
Accepted

### Implementing the Biham–Middleton–Levine traffic model as CellularAutomaton

The following code simulates the Biham-Middleton-Levin traffic model for 1000 iterations using explicit rules. According to Wikipedia the blue and red cars take turns to move, which means each step is ...
• 68.9k
Accepted

### Use a picture as the initial distribution of an agent based model

You have to use ColorNegate and other image processing functions to make the area that you want to sample is white, while the rest is black. After that you can use <...
• 68.9k

### Large deformation of solids

It is not 2D problem, but 3D problem. So we actually need some 3D model to describe deformation. But before do this, we can describe the problem in the beam theory. Fortunately, this problem has exact ...
• 34.7k
Accepted

### Large deformation of solids

I think you guys are using the wrong theory, as far as I understood the code above. Sadly I only have little time, and in this answer I can only give you the theory without code. If I read your code ...
• 5,283

### Mathematica Implementations of the Random Forest algorithm

As of version 10.0 there is a built in implementation of Random Forests which is accessible through the Classify function. ...
• 10k

### My Girlfriend is going to prison...Save her with Math

I have no experience with what you are trying to do so this is entirely guesswork but maybe you want something like this? ...
• 265k

### Why does NonlinearStateSpaceModel linearise?

My guess is to be able to have the same internal representations as for linear systems. It is not possible to represent a system using A,B,C,D state space standard ...
• 113k

### Mathematica code for bifurcation diagram in 3D

Looks like a little three-species food web model -- a perfect excuse to use my new EcoEvo package. First, install the package (one-time only): ...
• 18.1k
Accepted

### Computing launch parameters for hitting a point in 3D with projectile under influence of wind

You may use NMinimize[] on the results of ParametricNDSolve[] like this: ...
• 114k
Accepted

### Why doesn't Mathematica completely draw the fit?

Add the option PlotRange (say PlotRange -> {{0, .006}, {0, 90}}), and use data2 as <...
• 350k

### Mass Transport Model

Thanks to @xzczd answer we can reproduce solution with FEM. First we should note that $[A]+[B]+[C]=[A]_{bulk}$ in a case of equal $D_A=D_B=D_C$, therefore we can exclude equation for $[A]$ and resolve ...
• 34.7k
Accepted

### Find fit of an experimental PDF

Pure GammaDistribution does not seem at all like a good fit even visually. You need probably a MixtureDistribution. You could ...
Accepted

### Find best equation for data and the area under curve

A curve that is a multiple of a gamma distribution seems to fit: ...
• 34.8k

### Use a picture as the initial distribution of an agent based model

you can use PixelValuePositions ...
• 8,568

### Solving Differential Equation System for HIV Treatment Model

Structuring the script. ...
• 3,643
Accepted

### Fitting multiple data with model and NDSolve with different initial conditions, and other shared parameters

The subject of parameter fitting comes up frequently on MSE. Parameter fitting is a difficult subject and will depend on your data quality, your model, and your intial guesses. I have been dabbling ...
• 16k
Accepted

### Find the best fit with some conditions

I'm not sure why FindFit can't manage it, but if I construct the objective function myself to minimize square residuals and I use ...
• 20.5k