Questions on the use of Mathematica to construct models for approximating empirical data.

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4
votes
1answer
158 views

TimeSeriesModelFit incorrect?

I am trying to determine the optimal model for time series data (1592 observations). When I run TimeSeriesModelFit, Mathematica selects $AR(1)$ model, the estimated ...
1
vote
2answers
225 views

How to Fit experimental data with 4D ParametricNDSolve?

Let me first explain the background problem. I'm trying to solve a problem with a projectile motion in 4D such that the position vector is: $\boldsymbol{r}(t)=\boldsymbol{r}[x(t),y(t),z(t)]$ I have ...
5
votes
0answers
98 views

Custom Methods for NMinimize/NonLinearModelFit

Is there a way to write custom methods for NonLinearModelFit or NMinimize? To give background, I currently have a batch of code ...
1
vote
2answers
104 views

NonlinearModelFit and plot with multiple parameters function

i ve got quite simple function: $f(t) = x1 * a(t) + x2 * b(t)$ and table of results like this one: t | f(t) | a(t) | b(t) ---------------------- 1 | 2 | 5 | 3 ---------------------- 2 | 4 ...
1
vote
0answers
54 views

Fitting a vector-valued model using Mathematica

I'm wondering if there is a way within Mathematica to perform some kind of parameter fitting on a vector-valued model function (in this case a model of electric field vectors). Essentially what I want ...
0
votes
1answer
79 views

How to do linear fit for 2D data points [closed]

I am very much new to Mathematica, and facing several difficulties. I used the following code Fit[{2, 4, 6, 8}, {1, x}, x] The output is ...
2
votes
1answer
81 views

Computing a Gamma function-Gaussian integral

I would like to compute the following function: Integrate[Gamma[k,0,Exp[-2 e x^2]],x] k is an integer and ...
-2
votes
2answers
56 views

How can I use NonlinearModelFit with multiple variables? [closed]

I am trying to find the coefficients for following equation: $\quad \quad f(x,\,y,\,z) = a (x^2)\, exp(b x + y^2) + c z^2 y$ using NonlinearModelFit. But I can't ...
1
vote
0answers
33 views

How does LinearModelFit handle cases where the design matrix rank is lower than the model terms?

So, I understand what this error means: ...
0
votes
1answer
75 views

Interpreting P-Value on ParameterTable

When using LinearModelFit[] we can generate a table of parameter values and statistics for the corresponding model using the property "ParameterTable". Looking in the documentation I can't find an ...
6
votes
2answers
288 views

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 ...
16
votes
1answer
515 views

Difference between Fitting Algorithms

I am new to Mathematica, and I don´t quite understand, what the difference between the fitting algorithms Fit, FindFit, ...
4
votes
3answers
182 views

How to fit parameters in a system of coupled differential equations

Problem description: I'm studying a chemical reaction that can be modeled by a system of coupled differential equations, and I want to use measured data to determine the parameters that appear in the ...
6
votes
4answers
404 views

How to fit a surface to 3D data in Mathematica?

I have a set of data coordinates which is mostly compatible with an Ellipsoid: {{x1,y1,z1},{x2,y2,z2}, ... , {xn,yn,zn}} Now I want to find the best 3d volume ...
2
votes
1answer
95 views

How can I get the coefficient of the exponent from a nonlinear model fit?

I have been trying for over an hour now to get the numeric value for "HalfLifeN" from the code in the screenshot below. Not to mention mathematica simplifies ...
0
votes
1answer
41 views

Using Check[] on multiple statements

I am using a loop to run run multiple fits. If a fit fails, I don't want it to either appear in my data or to affect later fits so I am using the Check[] function to catch if any errors occurred (I'm ...
2
votes
1answer
44 views

Is this behavior of DistributionFitTest together with StableDistribution a bug?

I have been using DistributionFitTest to fit the following data: ...
3
votes
1answer
138 views

NonlinearModelFit: fit a vector-valued function to a data vector

I have a vector of data points: data = 10 Sin[#/10] + RandomVariate@NormalDistribution[] & /@ Range[200]; And I have model that provides the complete ...
0
votes
1answer
108 views

How to adjust excel data for NonlinearModelFit?

I'm really new to Mathematica and I'm facing a problem and would really appreciate some help! Maybe my question is similar to one described in How to fit 3 data sets to a model of 4 differential ...
1
vote
1answer
45 views

Convert Dates to values on an X axis

I have a bunch of dates and values which I put into the DateListPlot to get a graph. However I would also like to put this information into the Fit or LeastSquares to estimate what the value would be ...
0
votes
0answers
30 views

How to use FindFit to find the parameter in Laplace space(numerically inverting Laplace transforms)

I am trying to find the parameter in Laplace space, and a very simple example is shown below: I have known the solution $y_{laplace}$ in the laplace space is $a/s^2$, and I also have some discrete ...
8
votes
1answer
308 views

How can I improve my prediction for the end time of the Reddit button game?

There is an April Fools game on Reddit where users with accounts can press a button (once) to reset a 60 second countdown timer: https://www.reddit.com/r/thebutton ...
0
votes
2answers
156 views

Log Linear Fitting of a data: e.g. {xi,Log [yi]} and plotting the fit

I have a Log-Linear plot, and i'm unsure about how to fit a line to it. The data represents a I (current) vs V (voltage) curve. The exponential portion of this curve (linear in a Log-Linear plot) is: ...
5
votes
1answer
160 views

FindFit returns “tensors have incompatible shapes”

I'm trying to fit experimental data with FindFit and implicitly calculated function. It seems, that function works fine and satisfactorily approximates data when parameters are fed manually. However ...
0
votes
1answer
74 views

How to determine a function that fits a geological model

I have a problem. I am currently working on a code that works by comparing data (real or synthetic) to an earth model (described by earth layers, or in this particular, velocity (...
0
votes
0answers
41 views

Why does ParallelMap throw errors where Map does not?

I am encountering a problem with ParallelMap. I have a call in a large code base, part of which attempts to fit data in parallel using ...
4
votes
3answers
107 views

Better output for NonlinearModelFit “ParameterTable”

The Standard table fo parameters of NonlinearModelFit is obtained from NonlinearModelFit[{{0, 1}, {1, 2}, {3, 3}}, a + b*x, {a, b}, x] %["ParameterTable"]] I ...
1
vote
1answer
60 views

Precision of starting values in FindMinimum [closed]

I am currently working on an optimization of chemical kinetic model. Starting points for FindMinimum are defined as: ...
1
vote
1answer
64 views

Wrong fit with FindFit

I have a set of data (Datax for x-axis and Datay for y-axes) to fit to a sigmoidal function (Hill type). While Origin gives me the right answer, Mathematica does not. The fit values given by Origin ...
0
votes
0answers
45 views

Fitting an ellipse to data with a special constraint [duplicate]

I have a bunch of x,y scatter data and I am trying to fit an ellipse through them. I understand there are solutions for the fit where the data points are defined for a full or partial ellipse. ...
2
votes
0answers
69 views

ANCOVA (ANalysis of COVAriance)

I have two time series of the form {time, value} I have linear fits of each set individually, and I am interested in the statistical differences between the ...
0
votes
1answer
111 views

Simultaneously fitting two data sets to two functions is too slow [closed]

I have to fit two data sets to two functions(eps1,eps2) with same parameters (w0,f,g) Initially, I know only one function ...
7
votes
1answer
135 views
0
votes
2answers
66 views

Curve fitting of a list and exclude some figure

I am a fresher of Mathematica and trying to program a list of digits. When I plot the diagram of the list, it shows that the figure at 12 is much larger than the others. Does anyone have idea on it? ...
0
votes
0answers
99 views

Decompose Point-Spread Function into Seidel Aberration/Zernike Polynomials

I have measured the point spread function (PSF of a microscope) and I want to quantify it. For that purpose I want to fit my PSF data to the primary Seidel optical aberrations (or Zernike Polynomials, ...
0
votes
0answers
51 views

combining separate data into pairs after reading from excel so I can run regression

I have the following code that reads data from an excel spreadsheet: ...
0
votes
0answers
59 views

Fit a complicated function to a constant with NonlinearModelFit

I wish to fit a complicated parametric function (logder, with lambda parameters) to a constant (L) in order to minimize its dependence with the variable k in a given interval. To do that, I use a ...
1
vote
1answer
54 views

Fitting data with a complex function, but requiring real parameters

I am trying to fit a complex data with a complex function, with the real fitting parameters. I was trying to put there constraints like this, but I got error: ...
7
votes
1answer
290 views

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 ...
0
votes
2answers
61 views

Fitting data in form $f = f_0 + c A^x$

The Fit[] function in Mathematica can fit data in form of $f = f_0+c_1x+c_2x^2+...$ ($f_0$ and $c_i$ are unknown constants), is there a function can fit date in ...
3
votes
2answers
74 views

PredictionBands and the presence of {0,0} point

We know from this post, that the default fitting method cannot handle data with a {0,0} point, and that there are alternative methods. But, with these alternative methods, the prediction bands ...
1
vote
1answer
90 views

Fitting Legendre polynomial - Integer constraints in Fitting functions

I have some data in the form of {theta,y} and I am trying to fit a Legendre polynomial to it, however I don't know how I can get it to vary the m and l parameters in integer increments as I don't know ...
4
votes
1answer
95 views

FindFit runs extremely slow for my Function,how do I optimize this?

My function is the first order Bessel Function, and I am basically just trying to get this to fit in a way that does not take forever. I define the function as follows, (it seems to work faster if I ...
2
votes
1answer
66 views

LogitModelFit bias term when using design matrix

I'm using the LogitModelFit function with a 32-columns design matrix and 0 or 1 output vector: LogitModelFit[{datax, datay}]. ...
1
vote
2answers
70 views

Encoding variables

I'm trying to fit a Logistic Model using LogitModelFit in Mathematica. The data I'm using contain qualitative variables that I have to encode. I've searched in ...
1
vote
0answers
33 views

Fit a custom process to a data: inhomogeneous 2-state Markov chain

I would like to fit a custom process - a time inhomogeneous 2-state Markov chain, to data. The time inhomogeneity is a result of the transition probabilities varying sinusoidally through time with a ...
0
votes
1answer
48 views

NonlinearModelFit returning unexpected result

I am attempting to perform a weighted fit of some data. The Fit function produces the correct quadratic fit, which I am fine with, but it does not appear to support ...
2
votes
2answers
96 views

How to do dynamic range selection for data fitting in Log plot?

In linear plot, this can be achived by Locator like this: http://mathematica.stackexchange.com/a/24935/13580 ...
1
vote
0answers
81 views

How to control precision of parameters in NonlinearModelFit?

I am using NonlinearModelFit for fitting a dataset to some complex numerical model function that depends on a few parameters. The final required precision of these parameters is very low, like 3 ...
0
votes
1answer
49 views

ANOVA on data with different lengths

I have data in the following form: ...