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

learn more… | top users | synonyms (3)

0
votes
1answer
149 views

Fitting a function

I defined and evaluated a function Max2[t_?NumericQ] := Log[Abs[-1 + First[Maximize[sol1[[2]][x, t], 0 <= x <= L, x]]]]; Now, I expect this to be close to ...
1
vote
3answers
281 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: ...
3
votes
1answer
446 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 ...
1
vote
1answer
725 views

FindMinimum produces error message

I'm trying to solve a logistic regression problem using Mathematica -- more to improve my Mathematica skills than to solve the problem as I have already solved it using Octave. The problem I am ...
10
votes
1answer
1k views

How does Mma compute Confidence Intervals?

I am trying to understand how Mma computes the Confidence Intervals after a NonlinearModelFit. Consider the following example: ...
6
votes
2answers
255 views

Implement planar correction for skewed 3D profilometric data

I have some data that represents small-scale surface topography. The data is planar but not flat because it's impractical to level this microscope to a tolerance of microns. It looks like this: I'd ...
4
votes
0answers
219 views

Using FindFit to fit nonlinear ODE parameters, subject to a constraint (an inverse problem) [duplicate]

Similar to this post I am finding that constraints tend to make FindFit poor at finding a good fit. However, unlike the previous post, the constraints are required ...
6
votes
2answers
870 views

Find parameters of ODEs to fit solution data

Problem How to find the initial conditions x[0],y[0] and the optimal value of parameters a,<...
3
votes
2answers
537 views

fit a curve in a three dimensional space

I have a list of points of a curve in a three dimensional space, like ...
0
votes
0answers
45 views

How to fit ODE's coefficient, just like using NMinimize [duplicate]

I want to fit ODE's coefficients to a model. I tried using NMinimize, but it seems it does symbolic instead of numerical calculations. ...
2
votes
0answers
246 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 ...
3
votes
1answer
231 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 ...
1
vote
0answers
237 views

LeastSquares with some parameters missing

I want to do a partial least squares (PLS) regression using LeastSquares on my data. The input parameters are temperature, humidity and pressure for a given date. ...
4
votes
1answer
2k views

How does Mathematica estimate error on fit parameters?

When performing a fit using NonlinearModelFit (or any of Mathematica fitting functions, but I am particularly interested in nonlinear models), Mathematica makes a ...
13
votes
1answer
616 views

Does anyone have experience with performing symbolic regression using Mathematica?

I understand that there is at least one Mathematica package, DataModeler commercially available for symbolic regression. I'm seeking any observations with this or any other similar tool. I'm ...
0
votes
1answer
133 views

Curve Fitting Errors

I am trying to fit a part of a dataset to the function $$ae^{-b\sqrt{x-c}}$$. My friend was using GNUPlot to this and got reasonably good results. However when I try to this with Mathematica : ...
1
vote
1answer
183 views

Efficiency problem with least square algorithm (Error in both variables)

I was informing myself about the least square algorithms with errors in x and y. I found this post and the top answer wasn't ...
19
votes
4answers
2k 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: ...
4
votes
1answer
241 views

How to Use ProbabilityScalePlot with Censored Data?

I am trying to reproduce a ProbabilityScalePlot of censored data shown here (see Sample Analysis Plot). Here is my Mathematica code. First I deal with the uncensored case. ...
0
votes
1answer
71 views

LMS distance from a point to an InterpolatingFunction

I have a short script to NDSolve a second-order nonlinear BVP, which as its output produces an InterpolatingFunction object. I ...
2
votes
1answer
1k 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 ...
4
votes
2answers
793 views

FindFit for a differential equation model with multiple variables?

I'm trying to figure out how to use FindFit with a multivariable differential equation model and data. I've successfully made it work for the one-variable version ...
3
votes
2answers
2k views

How to enter an equation into FindFit?

I have the equation ...
6
votes
1answer
156 views

Why LinearModelFit is slower than NonlinearModelFit?

Why LinearModelFit is slower than NonlinearModelFit? ...
0
votes
1answer
159 views

fit recursive function to data

I have a function $g(x, n)$, which is a recursive expression: $x$ is a variable and $n$ the number of iterations. In my case $n=3$ for all $x$. An example is the following: ...
3
votes
2answers
583 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 ...
2
votes
1answer
4k views

Problem with NonlinearModelFit: “The function value… is not a list of real numbers…”

I'm trying to use NonlinearModelFit to fit the data: ...
9
votes
1answer
2k views

Measure length and diameter of objects in an image

I am new to Mathematica, and I am trying measure length and diameter of rectangular objects in an image. I wanted to fit rectangles in the objects, and then get the values. Can I do that with ...
0
votes
1answer
363 views

FindFit: why do I get negative value as result?

I am trying fo fit a model to data using FindFit. ...
6
votes
2answers
270 views

Transforming noisy multivariate data

I’ve been racking my brain all afternoon on trying to solve this… I have a set of noisy co-ordinate data data = {{x1,y1,z1}…..{xn,yn,zn}} that forms an ...
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 ...
2
votes
1answer
802 views

RSquared Mathematica Excel incoherence

I've done a NonLinearRegression with this data ...
0
votes
0answers
43 views

NonLinearModelFit not generating a model without the use of “BestFit”, not sure why [duplicate]

This is my first time using NonLinearModelFit and I have run into an issue that I can't find an explanation for. The fitted model contains a ...
1
vote
0answers
109 views

Can we ask ComponentMeasurements to use NonLinearModelFit to return a covariance matrix for underlying intensity data?

I'd like to be able to calculate a covariance matrix for some data underlying a morphological component. Provided this data, I can write something like: ...
5
votes
2answers
189 views
3
votes
2answers
358 views

How do I find the best fit?

I am trying to solve following system of three differential equations ...
1
vote
2answers
333 views

Plotting a dynamical NonlinearModelFit Function

Currently I'm playing around with dynamics and the NonlinearModelFit function. To be precise, I want to fit a function the data, which range I want to specify ...
23
votes
4answers
1k views

Generating an “average curve” from a dense set of “semicontinuous curves” which clear trends

This question is related to a previous one of mine: Partitioning a superset of coordinates into subsets that generate continuous curves, where the challenge was to partition a data set into two ...
3
votes
1answer
683 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 ...
1
vote
0answers
2k views

How to Output Chi-Squared Statistics when using NonLinearModelFit

I am using NonLinearModelFit for some curve fitting and I was wondering if NLM is able to output chi-squared/leastsquared statistics from the best-fit parameters and confidence intervals. From my ...
1
vote
1answer
144 views

How to find best MLE using `FindDistributionParameters`

This question is an extension of this question, if we change the initial values ...
0
votes
2answers
243 views

Why Do I Have Large Error Margin Using NonLinearModelFit function

Data {2.5984*10^-56,1.2266*10^-25,2.77402*10^-19,1.14182*10^-15,3.43647*10^-13,2.46313*10^-11,7.13917*10^-10,1.11045*10^-8,1.09754*10^-7,7.68589*10^-7,4.10723*10^-6,0.0000176576,0.0000634956,0....
2
votes
1answer
496 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 ...
20
votes
2answers
4k views

How to fit 3 data sets to a model of 4 differential equations?

I'm a biologist and a newbie in Mathematica. I want to fit three data sets to a model consisting of four differential equations and 10 parameters. I want to find the parameters best fitting to my ...
4
votes
1answer
2k views

How to make a multi-peak histogram fitting

I got a multipeak histogram from my data and want to fit it using a Gaussian Distribution function. ...
5
votes
2answers
870 views

Numerical Integration as Model for Nonlinear Fit

I'm trying to do a fit for parameters of a function within an integral but I'm getting errors when I try and run it. Essentially I want the following fit to work out: ...
2
votes
3answers
173 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 ...
1
vote
1answer
2k views

Keeping Nonlinear Model Fit Real

So I am using the NonlinearModelFit (NLM) command with a fairly simple function. There are 4 unknowns and the (x, y) points that ...
3
votes
1answer
101 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 ...
20
votes
0answers
893 views

Nonlinear least squares on a GPU with Mathematica 9

Update: A Mathematica wrapper for (https://github.com/zitmen/cuLM) should allow for us to directly implement the Levenberg-Marquardt algorithm in CUDA for nonlinear least squares fitting. In a ...