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

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4
votes
1answer
198 views

Find a Fourier series from discrete data

I am trying to fit a Fourier cosine series to discrete data. I read through this, but I was not able to understand it. The data should be periodic with a period of $0.2 \text{ m}$, and it is the ...
5
votes
1answer
75 views

Sensitivity of NonlinearModelFit to model

I have come across a circumstance where NonlinearModelFit is very sensitive to the model used. I am aware that NonlinearModelFit ...
5
votes
3answers
134 views
3
votes
1answer
55 views
0
votes
0answers
72 views

Fitting Data using GeometricBrownianMotionProcess

I am trying to fit Data (see below) using a GeometricBrownianMotionProcess, and have attached two figures. One figure is that of the Data, and the other of the GeometricBrownianMotion for given ...
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 $\sigma=0.1$: $W_t = \rho W_{t-1} + (1-\rho) \bar{W} + \epsilon_t$ ...
1
vote
1answer
85 views

Fitting with roots of transcendental equation

I'm new to this community and my first question probably reflect my lack of confidence with Mathematica. My problem is the following: I find the roots of a transcendental equation dependent on a ...
3
votes
2answers
64 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 ...
4
votes
0answers
89 views

Goodness of Fit of Copula Distribution

I am trying to find out goodness of fit of copula distribution, but Mathematica 10 gives me the same answer for each copula type. e.g ...
1
vote
1answer
101 views

Why does FindFit work and NonlinearModelFit does not?

I have a somewhat complicated function that I have defined. ...
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
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 ...
0
votes
1answer
99 views

How to speed up NonlinearModelFit applied on a NDSolve solution?

I'm trying to perform fittings of a model defined through a system of ODEs to data consisting of time courses of a measured quantity. As described in a previous question, the system of ODEs is as ...
1
vote
1answer
109 views

non linear Least Squares with model function given by ODE's

I have to fit to experimental data a model function given by a linear combination of functions y1(t) and y2(t) a1*y1(t) + a2*y2(t) with a1 and a2 ...
2
votes
2answers
124 views

BSpline or other curve through arbitrary ordered sequence of two-dimensional points

How does one create a BSplineCurve or other smooth curve passing through each point in an ordered list, where the curve may be non-simple, i.e., can double-back ...
2
votes
1answer
151 views
2
votes
1answer
79 views

Fails to apply NonlinearModelFit on a numerically evaluated model defined as a system of ODEs

I call for your help with because I'm getting troubles to fit a model defined through a system of ODEs. The system of ODEs is as follows: ...
5
votes
1answer
100 views

FindFormula can't deal with the population data from Wolfram server

Bug introduced in 10.2 and persisting through 10.2 or later In the documentation of FindFormula, the first application of it is to predict the population of ...
0
votes
0answers
170 views

Extracting parameters from a fitted function

Let's say I have written a function which performs convolution and returns value calculated for the time, t. ...
5
votes
1answer
120 views

How are p-values in fittings estimated?

I am trying to understand how p-values retrieved in a ParameterTable estimated but I couldn't find any specific information in the documentation about this. For instance, considering ...
0
votes
1answer
80 views

Binomial Regression where n > 1

I am not well versed in Generalized Linear Models, but am trying to use this approach to model some discrete data. I have binomial data where the sample size for each observation is the same size, ...
1
vote
0answers
69 views

NonlinearModelFit::nrnum error [closed]

I'm trying to fit data (including some small negative numbers at both extremes) to a normal distribution. ...
-1
votes
1answer
59 views

Pulling variable out of NonlinearModelFit [closed]

I have a fit, Dynamic[f1 = NonlinearModelFit[d1, a Exp[-(b (x - c1))^2] + yoff, {a, b}, x]] Where I need to be able to access ...
3
votes
2answers
98 views

Gauss Fit to List of 2D Points

I've been trying to find a solution to what I think is a common problem. I have a list of Data like ...
27
votes
2answers
484 views

What is behind Mathematica's experimental `FindFormula` function?

In version 10.2 there is a new experimental function: FindFormula. I suspect that a genetic programming algorithm (symbolic regression) is behind this new feature ...
13
votes
4answers
1k views

Implementation of smoothing splines function

I have some problems in writing a module for spline smoothing. Actually, I have been trying for about two weeks. My listing is here: ...
0
votes
0answers
56 views

Modify measured values to improve NonlinearModelFit results

Problem: Measured data points have a random distribution of DC offsets (either +/- 0.65 mV), that came from an incorrect setting on the 24-bit ADC we were using. Essentially for each measured voltage ...
1
vote
1answer
100 views

Problem fitting when some data is missing

I have a problem fitting a function to data, where I only have the falling and rising edges of the data, with the peak having been capped and was wondering if you have some tips. The data should have ...
6
votes
3answers
2k views

Find a best fitting curve for some data with no regular pattern

Suppose some data with no regular pattern is given, so common patterns of functions all fail to fit it. Then how can one find the best fitting curve? I believe there will be some data for which we can ...
16
votes
2answers
582 views

Curve fitting by running through hundreds of models and return the one with best fit

In the past, I used to solve a lot of my regression analysis (curve fitting) problems with a program called DataFit which runs on Windows. It has hundreds of regression models which it runs through in ...
0
votes
0answers
62 views

How to calculate the standard error of a parameter for a simple nonlinear fit?

I am trying to get the standard error of the estimate of a parameter in a simple nonlinear fit. I manage to get it for a linear fit. I used the formulation from a previous post. Here is my code for ...
3
votes
0answers
86 views
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
1answer
79 views

Still more problems with Fitting, please help

I'm in a little over my head here and I'm fully aware of it, so I'm hoping for some help. I've been assigned to a project where I am given data: http://www.pastebin.ca/3061136 (Example Data) I ...
2
votes
2answers
59 views

Using FindFit for a non-trivial complex function [duplicate]

I have data set which I would like to fit to the function $\quad \quad f(r) = A\cos(kr - \pi/4 + \phi_1)\times\exp(i(-2\log(r) + \phi_2))$, where $k$ is a constant I know and $(A,\phi_1,\phi_2)$ are ...
2
votes
1answer
68 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}]. ...
2
votes
2answers
64 views

Fit model with two dependent variables

Say I have an experiment that produces two values, for a given input. For example you get a complex response value. Now I have a model that - of course - also produces two dependent values for one ...
1
vote
2answers
88 views

TargetFunctions option in FindDistribution 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
71 views

Curve fitting data I imported from excel [closed]

This is my first time posting here, so sorry if I break any rules. There is this excel document from which I imported two columns of data to mathematica. I need to fit the data into a curve so that ...
0
votes
1answer
43 views

Mapping Linear Model Fit Over An Arbitrary Number of sets

I have multiple sets of data, and I want to apply Linear Model Fit sequentially to each set of data. For example, below tstlst contains 3 data sets. Right now I ...
13
votes
6answers
12k views

How to determine the center and radius of a circle given some points in 3D?

I was wondering if anyone could give me a hand with this problem I have. I have six points on a plane, and I am trying to determine if they form a circle or not. I know that any three points in 2D ...
3
votes
3answers
288 views

Fitting - Exponential

I'm trying to fit the following data using Mathematica, but unfortunately im not getting any decent results. ...
1
vote
0answers
95 views

Solution to heat equation with Neumann boundary conditions and lateral heat loss

I am conducting an experiment on heat conduction in a copper rod. To do so I am using a thin copper rod with several temperature probes, then I am going to compare the data with a solution to the heat ...
-1
votes
1answer
83 views

NonlinearModelFit errors and precision

For this problem, I use a data set, which I've made available here. ...
0
votes
0answers
39 views

R^2 values for piecewise regression

So I've used NonlinearModelFit on a Piecewise function and gotten a nice little piecewise regression. This is what my code looks like: ...
1
vote
2answers
83 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
2answers
70 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 ...
0
votes
0answers
28 views

Fitting problem: InterpolatingFunction can not be localised

I got simple data looking as follows {{541.447, 311752.}, {540.359, 311723.},.. I tried to fit it in mathematica for the first time with a function that usually ...
0
votes
0answers
35 views

Which one will gives best fitting result?

I want to find out the parameters A, B, and C of the ...