# Questions tagged [modeling]

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

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141 views

### Lagrangian of three-mass system with Mathematica

Before proceeding to calculations in Mathematica, I would like to clarify with knowledgeable people. There is an ordinary linear three-mass system. If we write its Lagrangian, we get the following ...
73 views

### Plotting fibre direction at each node

I was wondering if there was a way to plot the direction vector of a fibre family at each node in AceGen/AceFem? Below is an example of exactly what I want to do but I do not know how to recreate it. ...
48 views

### Modeling an XY positioning table that uses a cable-driven mechanism

I came across an interesting model on the MathWorks site. It's an XY positioning table that uses a cable-driven mechanism. Can someone point me to an example of such a mechanism done in Mathematica or ...
78 views

### Logistic fit of data

I would like to use LogitModelFit to find the logistic function to my data. The error I obtain is LogitModelFit::binrsp: The response values are expected to be ...
64 views

### Recommended model for hysteresis

I have a fabric-based strain sensor and would like to find out what other recommended models can be used in the hysteresis modelling. I have tried using the cubic function for loading and unloading ...
224 views

### Mathematica code for bifurcation diagram in 3D

Good day. I need help with the code in mathematica to plot the bifurcation diagram (e vs z*) or (e vs x*), for the system ...
44 views

### Combining fitted parameters to make a variable and telling me the error in it

I've fit my set of data to a function of the form: $a*\cos(2\pi t)+b*\sin(2\pi t)+c*\cos(4\pi t)+d*\sin(4\pi t)+e$ with a nonlinear model fit. The parameters $a,b,c,d,e$ have errors in it that ...
116 views

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

I have a question, and I really need your help, because I think I'm not understanding the reason... I have a potential model.. F[x_] := k x^n for the next ...
106 views

### How to create model for classification using SVM methods?

I have a matrix for diseases associated to their symptoms, the columns represent symptoms each row is a disease. the labels 1 and 0 in the matrix data sets represent when a disease i related to ...
114 views

### PIDTune and characteristic equation of zero

I have a BLDC electric motor, I'm currently trying to control via a PIDTune. This is mostly an attempt to reduce (remove) a small run away drift that ends up ...
217 views

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

I know that there are already questions about fitting multiple datasets and about NDSolve and about shared and non shared parameters, but I tried to apply them and some things are still not clear. ...
103 views

### Estimating parameters on system of differential equations

I am looking for some help estimating the parameters of a series of differential equations to assist fitting the experimental data I have collected. The Problem: The equations are based off of the ...
72 views

### Speeding up the calculations by Reduce and NSolve

I have a non-linear system of equations with numeric parameter values as shown below. I first tried FindRoot with given initial values and it did not converge. Then ...
151 views

### Physics based predictive model using Predict

Summary: The first order response of a block of metal quenching in a fluid (or a cold block heating in a warm environment) is well known. I am trying to create a physics based predictive model for ...
81 views

### Fitting data with 3 linear fits

I have a dataset that can be easily approximated by a piecewise function composing of 3 linear functions, but i am unable to get an accurate fit once the third linear function is required. The model ...
275 views

### Solving Differential Equation System for HIV Treatment Model

I was working on a project about optimal strategies for HIV treatment, models used from [Butler, Kirschner, and Lenhart] 1997. This model explains the spread of HIV viruses in the human body, where ...
51 views

### Fit data with a given function depending on parameters

I want to fit the data of a star's temperature with a function from a model. That function depend on several parameters. I want to know how can I find the value of those parameters. The data is: <...
160 views

### Model fitting for concave curve: test if asymptote or convergence exist

I am asking a double check if conceptually I set up proper model and proceeding in good direction to drive conclusions. I have a distribution that looks like this: I want to test if for increasing x ...
783 views

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

I migrated a numerical model code from Python to Mathematica and am surprised how much faster the Python version runs. Profiling of the Python version tells me that it is about 100 times faster (120 ...
134 views

### Fitting two equations to diferent parts of the same dataset

I have a system that transit between two different states. Each state output varies linearly with time, given by $m t+c$, where both lines intersect the $x$ axis in the same point. The output of this ...
77 views

### Finding the limit of a function

I have the following code: ...
70 views

15k views

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

Salacious title, but true story. ...
737 views

### How do I properly use Sow and Reap within a Do loop?

The problem is that reap only returns one value when I was expecting a string resulting from Do. For context: This is a simple democratic deficiency model. Where m is the number of periods, n is ...
538 views

### Non-linear-Model-Fit problem in mathematica

I have written the following code to fit the function g2 to data (a,b,c,d) but I don't realize where I have made a mistake,without ...