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

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5
votes
1answer
1k 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 ...
7
votes
0answers
134 views

FindFormula Control [closed]

FindFormula is great start on the path to full symbolic regression and I realize it's level of development is only experimental at this stage. But if I happen to ...
1
vote
0answers
49 views

Evaluation of likelihood very slow

I am trying to implement a simple statistical model for the first time in Mathematica. My model is made my one random variable which is the sum of background and signal. Background is an exponential ...
2
votes
0answers
859 views

histogram fit for probability density [closed]

I am trying to fit the (probability density) histogram of some data with the exponential function, but I am having difficulties. My raw data are in file called ...
1
vote
1answer
169 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 ...
15
votes
1answer
428 views

Using perpendicular offsets in FindFit

I want to use perpendicular offsets in the built-in FindFit function. Are there any possible ways or do I have to code everything by myself?
10
votes
1answer
331 views

Fittting data with combination of an unknown number of Gaussians

I have data that I want to fit with a constant plus a combination of Gaussians, with their actual number being one parameter of the fit (besides the average and the variance of every one of them). ...
7
votes
3answers
203 views

Fitting data with interdependence

I have an issue, of which I'm not sure it can be solved, with or without Mathematica. I feel as if it should be possible, but I'm quite clueless as to how. Some introduction is required. I'm working ...
0
votes
1answer
58 views

Extract coefficient from LinearModelFit [closed]

I want to know how to extract the coefficients from the result of LinearModelFit. The functions used to fit are complicated and being in different forms. For ...
19
votes
2answers
417 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 ...
6
votes
1answer
94 views
3
votes
2answers
192 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 ...
1
vote
1answer
171 views

Linear Fit of multidimensional data

I am trying to find linear decomposition of vector B (of arbitrary dimension $n$) in the form : $B = \alpha_{1} C_{1} + \alpha_{2} C_{2} + ...$ where $C_{i}$ are known vectors (of dimension $n$) ...
3
votes
2answers
258 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 ...
0
votes
1answer
105 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, ...
5
votes
1answer
528 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 ...
7
votes
3answers
175 views
3
votes
1answer
60 views
3
votes
2answers
148 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 $\sigma=0.1$: $W_t = \rho W_{t-1} + (1-\rho) \bar{W} + \epsilon_t$ ...
2
votes
1answer
138 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 ...
4
votes
2answers
106 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
173 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 ...
2
votes
1answer
173 views

Why does FindFit work and NonlinearModelFit does not?

I have a somewhat complicated function that I have defined. ...
3
votes
0answers
161 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 ...
0
votes
1answer
151 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 ...
2
votes
1answer
209 views
2
votes
1answer
107 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: ...
0
votes
0answers
512 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
247 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 ...
1
vote
0answers
120 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
74 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
722 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 ...
0
votes
0answers
74 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
118 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
3k 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
679 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 ...
3
votes
0answers
101 views
2
votes
3answers
382 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
112 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
94 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
76 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}]. ...
4
votes
2answers
252 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
105 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
188 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
57 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 ...
14
votes
6answers
14k 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
1k views

Fitting - Exponential

I'm trying to fit the following data using Mathematica, but unfortunately im not getting any decent results. ...
1
vote
0answers
256 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
197 views

NonlinearModelFit errors and precision

For this problem, I use a data set, which I've made available here. ...
1
vote
2answers
162 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. ...