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

learn more… | top users | synonyms (3)

2
votes
2answers
69 views

FindDistributionParameters gives an error for a mixture of user defined sinh-arcsinh distributions

I have some data (1593 values). I first binned it using the Knuth rule and fitted a function that is a linear combination of two sinh-arcsinh functions. I then ...
2
votes
1answer
124 views

How do I find out what a Mathematica function is doing (which numerical method it uses and how)?

Long story short, I am working on a project which entails fixing a bug I have found in Mathematica (8 and 10). In general, I would like to know what a specific Mathematica function is actually doing ...
2
votes
2answers
1k views

Line of best fit on LogLog plot

I have a LogLog plot, and i'm unsure about how to fit a line to it. The data represents a calibration curve. ...
2
votes
1answer
351 views

non-linear trend reduction using thresholds

Doing some mappings of the earth magnetic field results in the left-hand figure below (which consists of 181 profiles): To improve this I tried a non-linear trend reduction using, for example, ...
2
votes
1answer
76 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
1answer
60 views

Is there a way to show some “weighted” residuals after LinearModelFit?

I am fitting some functions to some data and then I want to analyze the residuals of that fit. I'd like to see how those residuals compare to the values of the original data, hence my "weighted" in ...
2
votes
1answer
135 views

Piecewise conditions with a parametric PDE

I'm using ParametricNDsolve to check best fit of a model (function Eb1) with some data, and I have four free parameters I want to test. I can easily construct a Parametric solution between the two ...
2
votes
1answer
104 views

nonlinearnodelfit with a matrix as weights

I have to fit a non linear model to my data and I am trying to use nonlinearmodelfit. The problem is that I have systematic errors, so the ...
2
votes
1answer
84 views

is there an option for FitResiduals in FindFit?

I know this option exists in NonlinearModelFit and probably in other fit models as well but for some reason the best result i get is with FindFit. Regards Doron
2
votes
1answer
198 views

Judging the quality of fitting an EventData object to a distribution using LogRankTest

I have $389$ data points defined in an EventData object and want to judge the quality of fit of this data to a fitted $3$-parameter Weibull distribution. This ...
2
votes
1answer
356 views

Problem with Covariance Matrix Output in NonlinearModelFit

I am running NonlinearModelFit based off of some simulated data and trying to fit to a function with more than one parameter. Eventually, I would like to fit to 5 ...
2
votes
0answers
64 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 ...
2
votes
0answers
54 views

Kalman filter estimation

Does anyone have any examples of the estimation of Kalman filters in Mathematica? I am new to these filters and struggling to compose the likelihood function. Some examples would be really helpful. ...
2
votes
2answers
159 views

RSquared: LinearModelFit vs NonlinearModelFit

I'm trying to understand the differences between LinearModelFit and NonlinearModelFit. One thing I notice is that the computation of AdjustedRSquared seems to be different, even when the model results ...
2
votes
0answers
54 views

Is there a way to produce a FittedModel object as the solution to a regularized regression?

I can get the Ridge or Tikhonov regression solution to Y = \[Beta].X easily enough as ...
2
votes
0answers
170 views

Power::infy: error using FindFit [closed]

I have a 2D data to fit (the Airy type pattern from diffraction of Gaussian beam on the circular aperture). Please see the attached picture. I was going to use a function like ...
2
votes
0answers
69 views

Why do EstimatedDistribution and DistributionFitTest work this way

I am fitting some time-series data to both a stable distribution and a normal distribution in order to assess the goodness of fit of each. Along the way I encountered the following confusing result. ...
2
votes
0answers
365 views

Speeding up Nonlinearmodelfit by constraining parameters?

I have a complicated parametric PDE that can be fitted to some data with NonlinearModelFit, but takes several hours to estimate the best values of the four free parameters. Currently, the code ...
2
votes
0answers
186 views

NonlinearModelFit is not giving the fit with minimum chi^2

First of all, a bit of background, I am using Mathematica to fit angular distributions of gamma rays, so I apologize for some of the serious messiness in the formulas. The data is simple I have three ...
2
votes
0answers
763 views

Linear regression with x and y errors

I have a question about finding a linear regression weighted with x and y errors. I found the answer provided by 0x4A4D in Estimate error on slope of linear regression given data with associated ...
2
votes
0answers
358 views

NonLinearModelFit with Two Dimensional List of Weights

I'm currently trying to fit Planck's law (B[λ, T]) to measurements, thereby determining Planck's constant. I have a list of triplets containing wavelength, ...
2
votes
0answers
812 views

ParametricNDSolveValue or NDSolve + fitting

I have been trying to find the value for the parameter kestim that yields the best fit of a model to some data points. datac has ...
2
votes
0answers
222 views

How to predict some constant number of values with NeuralNetworks

Example: << NeuralNetworks` data = {Sin[#]} & /@ Range[0, 4 Pi, 0.5]; learn = data[[1 ;; 15]]; Now, lets fit our neural network: ...
1
vote
2answers
181 views

Is it possible to monitor the sum of squared errors in a NonlinearModelFit or FindFit procedure during the process?

Since fitting procedures using NonlinearModelFit (or FindFit) sometimes take very long, I would like to monitor the sum of ...
1
vote
2answers
190 views

FindFit giving weird values on a logistic equation

I was trying to fit a set of data onto a logistic equation, however it ended up telling me that the initial value when $t=0$ is greater than the maximum limit, thus I am led to believe that it isn't ...
1
vote
1answer
1k views

How to find local minima of a multivariate function with singularity?

I am working on a logistic regression problem which requires minimizing a cost function J[{theta0, theta1, theta2}, X, y] to find the optimal value for fitting ...
1
vote
3answers
1k views

Why does FindFit seem to have trouble fitting exponential data?

I have 4 data points. t is in minutes, and y is radioactive counts per minute. When I input the following lines: ...
1
vote
2answers
1k views

Finding a best fit curve and plotting it [closed]

I have a list as shown below: m01 = {{250, 0.083121}, {200, 0.0888446}, {150, 0.0992422}, {100, 0.121567}, {50, 0.186825}} I'm new to Mathematica, and would like ...
1
vote
2answers
68 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
1answer
196 views

How do I construct a non-linear model from experimental data?

I want to find a function $w=f(x,y,z)$ that fits experimentally determined values of w. For example, assume ...
1
vote
2answers
61 views

TargetFunctions option in FindDistrobution yields error

I have some data set that I am trying to find the maximums . I figured I could do this by fitting the many peaks of the dataset to Gaussian distributions and then finding the peaks of this data from ...
1
vote
1answer
184 views

how to find curve fitting parameters without an explicit relation between x and y?

Let's say I have some experimental data (x,y) and I want to find some fitting parameters. But in my mathematical model, the fitting parameter are not in a simple equation that relates x and y. For ...
1
vote
1answer
966 views

FindFit: getting confidence intervals for the returned parameters

I'm using FindFit[] to fit a function to some experimental data. I'd like to know what error bars are on the fitted parameters. Scipy's ...
1
vote
2answers
95 views

Does FindFit use symbolic differentiation?

Does FindFit use symbolic differentiation when optimizing by least squares a non-linear function?
1
vote
1answer
188 views

Fitting data to a circle with FindFit

I'm currently trying to use the Mathematica's FindFit command to fit a curve of some data to the bottom half of a circle. The data is of the form ...
1
vote
2answers
162 views

How to fit exponential function which is not converging

I performed an experiment where I measured diffusion in a lipid bilayer. I performed the measurement by fluorescently labeling some molecules in the bilayer, and the irradiating them with light ...
1
vote
2answers
355 views

Can't find a fit for Erf

I have the following numbers ...
1
vote
3answers
229 views

Getting an equation of particular curve

How can I get an equation of the similar shaped curve? I've tried to get it like y = a + c x^2 + d x^3: ...
1
vote
2answers
64 views

What is the role of the pattern object in this implementation?

In the documentation I found a nice idiom which allows me to do model fitting with interpolating functions. I think this kind of thing is amazing and a credit to the utility of an environment like ...
1
vote
1answer
50 views

Trouble fitting with NonlinearModelFit

I'am having a bit of a headache comparing the results from the NonlinearModelFit to a particular dataset. I have the following dataset, ...
1
vote
2answers
213 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 ...
1
vote
1answer
209 views

General F statistic and p value in LinearModelFit

Many statistical packages provide a "F statistic" and the corresponding p value in their output of a multiple linear regression. I don't find that in the parameters of the Mathematica function ...
1
vote
1answer
185 views

show fit information on plot

After performing a fit in Mathematica, I would like to show the fitted parameters in a box on the plot showing the fitted function. How would I go about achieving that? Here is a MWE: ...
1
vote
1answer
208 views

NonLinearFit with “complicated” integral model

I have a set of data $y_i (z_i)$ with errors $\Delta y_i$ ...
1
vote
2answers
111 views

Minimizing the maximal residual in mathematica

With this: d1 = 10; d2 = 4; mat = RandomReal[{-1, 1}, {d1, d2}]; vec = RandomReal[{-1, 1}, d1]; LeastSquares[mat, vec] ...
1
vote
2answers
98 views

How can I get a fully functional FittedModel when fitting data to a pointwise function?

When I am fitting data with a pointwise function using NonlinearModelFit, the produced FittedModel fails to calculate variances ...
1
vote
1answer
498 views

Fitting parameters of user defined function returning discrete values

So, I'm fairly new to Mathematica (apologies in advance for the noobiness), and I'm having some problems regarding fitting the parameters of a user defined function to data. I'll give a representative ...
1
vote
2answers
75 views

Non Linear Model Fit (Division by Zero Error Message)

Can someone please tell me why this expression returns error messages about division by zero. ...
1
vote
1answer
82 views

Plotting data after fitting it to exponential function [closed]

I am trying to plot h vs t such that h fits a equation ...
1
vote
1answer
77 views

Find the best fitting function for some experimental data

I am almost new in Mathematica, and so I have some problems that may appear basic for you. I am given a set of data taken from an experiment. I am supposed to find the curve that best fits them. The ...