Questions tagged [fitting]

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

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1answer
141 views

Replicating Excel output using Mathematica

I have 2 columns of data in Excel. One is inputs the other is outputs. I ask Excel to make a graph of that data and to fit the data to a power trendline. Excel does this and it's fine as far as it ...
2
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2answers
981 views

Can't find a fit for Erf

I have the following numbers ...
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2answers
143 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 ...
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1answer
102 views

Constraining some rows from LeastSquares to lines

For two matrices, A and B, with dimensions {n,p} and ...
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1answer
209 views

Find Numerical Derivatives (With Errors) given some data

I have a question. Suposse I have some data with their respective errors: ...
9
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1answer
662 views

Least Square Data Fit /Design Matrix

I am trying to learn how to use the DesignMatrix function in Mathematica and how to perform a LeastSquares fit. I am at end of ...
3
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2answers
563 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 ...
4
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2answers
413 views

Multi-Fitting with Nonlinear model

I want to fit experimental data by the H-N model. Here is the H-N model: $$\text{EHN}(T)\text{=}\text{E$\infty $}+\frac{\text{E0}-\text{E$\infty $}}{\left(1+\left(i \omega\tau(T_g)10^{-\frac{\text{C1} ...
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2answers
1k views

Fitting a beta distribution to a probability density curve

If I have a spectral data set showing measured energy on the y-axis and frequency on the x-axis, how would I go about fitting this to a beta distribution? For example, lets say I had the data for the ...
3
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1answer
245 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: ...
2
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1answer
1k views

Fitting data using a differential equation

I have data generated from two functions given below. How can I go about finding a fit of the form: y'[x] == -(a + b/(c + d y[x] + e F[x] )) where a,b,c,d,e are ...
5
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3answers
577 views

Determing two Nonlinear model fits with 95% confidence bands from one data set

I have the following data which is postulated to have contributions from two different sources .....as can be seen from the confidence band, many points are out of the band. Question: How can I ...
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2answers
324 views

Any other way to get a better FindFit for my data besides good initial parameters?

I fit some data with FindFit and NonlinearModelFit with some constraints and I am not getting a good fit with my data. I read ...
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1answer
969 views

Curve fitting data to model

Example Assumptions: ...
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4answers
2k views

Estimating a distribution using binned data

I have data from which information has been irretrievably lost through binning and I am trying to find a plausible distribution from which it derives. There is an academic paper suggesting that the ...
4
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1answer
588 views

Fitting triangular function with HeavisideTheta

I have a problem fitting a triangular function (like potential vs. time in cyclic voltammetry) with a HeavisideTheta function. I just want to get used to ...
1
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1answer
279 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
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1answer
542 views

dynamically set fit parameters and models with FindFit

I want to fit a gaussian profile by setting some values dynamically, but FindFit returns an error and i can't see the problem. with a given gaussian: ...
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1answer
105 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
4
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1answer
850 views

FindFit not giving a good fit despite good initial parameters

I'm having a problem with FindFit not giving a good fit to my data, even though the initial parameters I give look really good when plotted. The fitting function is ...
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0answers
386 views

Using FindFit for step functions

Having used FindFit like so: ...
6
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2answers
333 views

how recover lost data of coordinates from contourplot of mention data?

I have made Contour Plot for a lot of data, like this ...
9
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1answer
3k views

What exactly is “ParameterErrors” of NonlinearModelFit?

I am trying to get what I call a "$\chi^2$ fit". This means taking a function $f(x,p)$ of the variable $x$ with a parameter $p$ and finding the value of $p$ that minimizes the "distance" from a data ...
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2answers
787 views

How to solve this FindFit::nrlnum:

the following code show error message FindFit::nrlnum: "The function value {6.71759 -9.36268*10^-8\ I,6.51797 -8.42641*10^-8\ I,6.31789 -7.49014*10^-8\ I,6.1179 -6.55387*10^-8\ I,5.91794 -5....
5
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1answer
1k 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. ...
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1answer
1k views

Fitting a Function With a Numerical Integral [duplicate]

I am having trouble using FindFit with the following function. ...
6
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1answer
2k views

Having trouble fitting data using NonlinearModelFit

I'm trying to fit data = {{2002, 45000}, {2004, 90000}, {2005, 120000}, {2013, 211000}}; to an exponential function ...
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0answers
187 views

Smoothing a function

NDsolve gives me a solution to a certain NL PDE. I want to evaluate the rate of exponential decay of the maxima of the solutions in time. So, I plot ...
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1answer
184 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 ...
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3answers
601 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: ...
4
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1answer
654 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 ...
2
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1answer
1k 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 ...
12
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1answer
2k 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
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2answers
330 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
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0answers
278 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 ...
7
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2answers
2k 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
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2answers
1k views

fit a curve in a three dimensional space

I have a list of points of a curve in a three dimensional space, like ...
3
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1answer
276 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 ...
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0answers
294 views

LeastSquares with some parameters missing [closed]

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. ...
5
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2answers
3k 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 ...
15
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2answers
927 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
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1answer
230 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 : ...
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1answer
416 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 ...
24
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4answers
4k 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
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1answer
364 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
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1answer
80 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
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1answer
2k 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
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2answers
1k 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 ...
5
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2answers
5k views

How to enter an equation into FindFit?

I have the equation ...
6
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1answer
223 views

Why LinearModelFit is slower than NonlinearModelFit?

Why LinearModelFit is slower than NonlinearModelFit? ...