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

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3
votes
2answers
75 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 ...
3
votes
1answer
134 views

Troubles with FindFit for ODE

I need to use FindFit for ODE with arbitary number of parameters. This code (from documentation) works: ...
3
votes
2answers
1k views

How to enter an equation into FindFit?

I have the equation ...
3
votes
1answer
2k views

Combined fitting via NonlinearModelFit

I am trying to fit my data to a combined function model. Say I have two functions with some common parameter(s) f[x_]:= a*x^2 + b*x + c g[x_]:= d*x^2 + e*x + c ...
3
votes
1answer
55 views

Is this behavior of DistributionFitTest together with StableDistribution a bug?

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

Test Goodness of fit for FindFit

Is there any way to get an estimate of the goodness of fit from FindFit, for instance getting the final error? The documentation doesn't provide any hints, and a quick Google search didn't return any ...
3
votes
3answers
199 views

Fitting the Plot by fourier Series of either sine or cosine

I have list of data and its plot and I don't know how to fit the plot with fourier series of either sine or cosine. Full Data: ...
3
votes
1answer
379 views

Fitting one function to another

I'd like to see how close I can fit an exponential function to a cosine function in the domain of $\;-\frac{\pi}{2}$ to $\frac{\pi}{2}$ in the least squares sense. ...
3
votes
1answer
96 views

How do I test for the occurrence of an error message and act on it?

I want to see how well some curves fit a data set. If a curve doesn't fit after 100 iterations, I get the error cvmit. How do I test for and handle this error ...
3
votes
1answer
556 views

How do I draw a credible velocity vs. time graph using Locators?

This is partly a math question, partly a Mathematica question. For educational purposes, I'm making a simple demonstration to create a velocity over time graph from six locators. On the basis of ...
3
votes
2answers
139 views

Automatically detect higher slope in numerical data (within a certain range)

Suppose the dataset data is part of some simulations whose results should follow a certain model. Here is data and its ...
3
votes
2answers
66 views

How to use Evaluation Monitor in conjunction with NonlineaModelFit?

I am trying to find out how many function, gradient and hessian evaluations are made when i run NonlinearModelFit for example in this case ...
3
votes
1answer
119 views

How to make a diagnostic plot for the regression?

Context I am interested in LinearModelFit, and would like to make diagnostic plots using Mathematica. I cannot find them in Mathematica document center. For example, the following R program makes ...
3
votes
1answer
570 views

NonlinearModelFit returning nonsense for very simple data

In fitting the following data, if I first log transform the y-values and use LinearModelFit I get a set of parameters that fits the data: ...
3
votes
1answer
1k views

Having Trouble Fitting Complicated Exponential Function with FindFit

I am working on high pressure shock experiments and am trying to figure out a the temperature of a sample under strong shocks. I have a measure value from 4 wavelengths of a pyrometer and am using a ...
3
votes
1answer
82 views

Ordinary Least Squares (OLS) with RLink

I need to calculate the parameters b0, b1 and b2 in: ...
3
votes
1answer
167 views

FindFit with parameters which are simultaneously in initial conditions

I have RLC circuit. I would like to find R and L by using FindFit, but L is in initial condition and I have problem with it. Could you help me ? ...
3
votes
1answer
151 views

Applying LinearModelFit[] to data obtained with WeatherData[]

I am trying to perform a linear regression on some weather data, but I can't seem to figure out how to perform the operation. What I have right now is this: ...
3
votes
2answers
207 views

FindFit “is not a real number” error when fitting a parametric function to the data

I am using Mathematica's FindFit function to fit a parametric solution to my data and I am getting the error ...
3
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. ...
3
votes
1answer
309 views

FindMaximum of loglikelihood in Gaussian Process

I am trying to implement a Gaussian Process and have problems to maximize the loglikelihood because the function consists of a determinant of a matrix that is dependent of 2 variables and the product ...
3
votes
1answer
89 views

Saving data from NonlinearModelFit

If you use NonlinearModelFit the results are put into some sort of output package. How do you save these packages so that you can go back to them later? My particular problem is that I generating ...
3
votes
2answers
434 views

SinglePredictionBands versus MeanPredictionBands from NonlinearModelFit

From my Statistics lectures I know the term confidence and prediction interval, whereas the confidence interval is smaller than the prediction interval. If I plot the mean and single prediction bands ...
3
votes
2answers
335 views

How do I find the best fit?

I am trying to solve following system of three differential equations ...
3
votes
2answers
130 views

Estimate parameters of AR1 process

I am trying to estimate the parameters of a series $Z_t=W_t^\beta$, where W_t follows an AR1 process with mean 2, $\rho=0.9$ and $\sigma=0.1$: $W_t = \rho W_{t-1} + (1-\rho) \bar{W} + \epsilon_t$ ...
3
votes
1answer
207 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 ...
3
votes
1answer
552 views

Generating a “best fit” curve to a set of noisy data corresponding to a moving object

Please note that this is an extension of a previous question: Interpolating a sparse list of two-dimensional coordinates We have an ordered array of coordinates corresponding to the position of an ...
3
votes
1answer
582 views

How to adjust parameters to experimental data on a NDSolve problem

I have 2 differential equations with 2 variables, x and y,which are a function of t and I have the parameters k1, k2 y k3. ...
3
votes
1answer
953 views

Error message from evaluating NonlinearModelFit

I am trying to fit data to a Morse potential using NonlinearModelFit as follows: ...
3
votes
0answers
86 views

How to find the best fit for given input data? [closed]

I have the following data: ...
3
votes
0answers
126 views

Fitting data to a complicated function

So, where to begin. I have a certain dataset that I want to fit to a function. However, the function is rather complicated (matrix inversions, linearsolve) and does in general not have a closed form ...
3
votes
0answers
88 views

Fitting data to plot using errors as weights

I have some enzyme kinetics data that I want to fit to the Michaelis-Menten curve in order to obtain the kinetic parameters of the enzyme. Is it meaningful, statistically and functionally speaking, ...
3
votes
1answer
157 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 ...
3
votes
0answers
135 views

The CorrelationMatrix is equal to corrcoef of Matlab?

How can I generate a matrix which is equivalent to the results of the "correlation coefficients" command (corrcoef) in Matlab? When I make a LinearModelFit, I can get a CorrelationMatrix, but is this ...
3
votes
0answers
160 views

Memory problem in Mathematica 10

I'm having a problem with memory. I'm doing nonliner fits of several data lists to a system of differential equations. When I evaluate the "Do" cycle the memory grows with the iteration step up to my ...
3
votes
0answers
319 views

To what extent can NonlinearModelFit be sped up?

Can NonlinearModelFit be parallelized or compiled to allow one to achieve a scalable speedup for a fitting procedure? Attempting to use this function to fit a ...
3
votes
0answers
386 views

Is it possible to marginalize one or several parameters obtained from fitting procedure?

Statistical model analysis package has a few fitting functions. Their arguments are data points, fitting model and parameters in the fit. The result is a set of best values for parameters, which ...
3
votes
0answers
218 views

Mathematica Complains about Non Symmetric Covariance matrix, when it's not the case

I was doing some fitting with Mathematica7 using NonlinearModelFit. It's quite long the program to do the fit and that's why I am not displaying here ... It goes ok, and I can get the fit parameters ...
2
votes
3answers
227 views

To obtain an equation for a given curve

I have obtained the graph, I would like to know its equation. The graph seems to be a hyperbolic spiral which, its equation reads, $r = a/\theta$. I read here and also, but these are concerning the ...
2
votes
3answers
185 views

Fitting and plotting Weibull distribution

How can I find the best fitted 2-parameter Weibull's distribution (PDF) to describe my data? How can i plot my data and estimated distribution all in one graph? How can I show/compare results of ...
2
votes
3answers
1k views

Plotting a list along with its trend line [duplicate]

Say I have these data: data = {{1, 3}, {2, 4}, {3, 6}, {4, 7}}; I want to fit these data with a quadratic equation, like this: ...
2
votes
2answers
127 views

Finding the FWHM of a NonlinearModelFit gaussian [duplicate]

I have a NonlinearModelFit in a very large program, f1 = NonlinearModelFit[d1, a Exp[-(b (x - c1))^2] + yoff, {a, b}, x] Which is used in my program to produce ...
2
votes
1answer
90 views

P-Values are inconsistent when using DistributionFitTest repeatedly

I am attempting to become more familiar with the DistributionFitTest, specifically the distributions it yields and their fittedness. What I have found is that when I generate random data, fit it, and ...
2
votes
2answers
119 views

FindFit working with Integrate but not NIntegrate - I am using “?NumericQ”

I'm having some syntax problems with finding a fit to an equation that doesn't have an analytical expression for it's integral. Because I think the problem is one of syntax, I am substituting a ...
2
votes
1answer
530 views

RSquared Mathematica Excel incoherence

I've done a NonLinearRegression with this data ...
2
votes
3answers
168 views

Removing of artificial sampling step effects

Look at this plot, it represents an underground interface between two formations, this interface should dip very gently left-downward, all the steps are artificial effects due to sampling. The natural ...
2
votes
1answer
101 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 ...
2
votes
2answers
382 views
2
votes
1answer
869 views

Nonlinear least squares

I have a typical nonlinear least square problem and it seems very similar to the example provided in the section on parameter fitting at the Wolfram website. Unfortunately I always get some error ...
2
votes
2answers
254 views

FindFit: Fit that is always lower - Change of Norm?

I am trying to find a fitting function for a multidimensional set of data. I will have to find a fitting function that is always lower (conservative) than the data fitted. The easiest way is to look ...