44
votes
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
28
votes
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
24
votes
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
21
votes
Accepted
Couple a PDE and ODE in NDSolve
Modified Newton Cooling Law implementation and reduced FEA cell length
...
- 7,247
16
votes
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
16
votes
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
14
votes
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
14
votes
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
13
votes
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
12
votes
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
12
votes
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
12
votes
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
11
votes
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
11
votes
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
11
votes
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
11
votes
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
10
votes
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
10
votes
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
10
votes
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
10
votes
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
9
votes
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
9
votes
Accepted
Why doesn't Mathematica completely draw the fit?
Add the option PlotRange (say PlotRange -> {{0, .006}, {0, 90}}), and
use data2 as <...
- 350k
9
votes
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
8
votes
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 ...
- 69k
8
votes
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
7
votes
Use a picture as the initial distribution of an agent based model
you can use PixelValuePositions
...
- 8,568
7
votes
7
votes
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
7
votes
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
7
votes
Accepted
Time dependent Schrödinger equation in 2D
Something like the following should do. It employ the finite element method.
...
- 96.4k
Only top scored, non community-wiki answers of a minimum length are eligible