Questions on the use of Mathematica to construct models for approximating empirical data. (FindFit[], Fit[], LinearModelFit[], NonlinearModelFit[], etc.)
3
votes
0answers
154 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
2answers
223 views
Finding a best fit curve and plotting it [closed]
I have a list as shown below:
m01 = {{250, 0.083121}, {200, 0.0888446}, {150, 0.0992422}, {100, 0.121567}, {50, 0.186825}}
I'm new to Mathematica, and would like ...
2
votes
2answers
99 views
How can I consistently get a good logistic regression fit?
I'm executing the command
NonlinearModelFit[data, c/(1 + a Exp[-b x]), {a, b, c}, x]
with the data being
...
2
votes
2answers
77 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 ...
2
votes
1answer
72 views
How to get confidence bands of parameters from a fitting procedure?
I have done fitting of data points with a given model that has two parameters (A and B), using NonlinearModelFit. The result of the fit is the maximum of the ...
2
votes
1answer
247 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
...
2
votes
2answers
221 views
Non-linear trend reduction with missing data
How can I reduce a non-linear trend of some data series if there are parts of "no data", represented by the value 99999? For example:
...
2
votes
2answers
66 views
Putting a matrix inside function
I want to fit a function to some data and inside the function there's a list
here's my data
...
2
votes
1answer
146 views
Problem creating MeanPredictionBands
I have a problem creating MeanPredictionBands for my function which I fitted using NonlinearModelFit. I have a complex-valued ...
2
votes
1answer
264 views
non-linear trend reduction using thresholds
Doing some mappings of the earth magnetic field results in the left-hand figure below (which consists of 181 profiles):
To improve this I tried a non-linear trend reduction using, for example,
...
2
votes
0answers
80 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 ...
2
votes
0answers
468 views
FindFit vs. NonlinearModelFit [closed]
Would anybody be able to elaborate on the difference between FindFit and NonlinearModelFit. I couldn't find any documentation ...
2
votes
0answers
159 views
How to predict some constant number of values with NeuralNetworks
Example:
<< NeuralNetworks`
data = {Sin[#]} & /@ Range[0, 4 Pi, 0.5];
learn = data[[1 ;; 15]];
Now, lets fit our neural network:
...
1
vote
1answer
313 views
How to find local minima of a multivariate function with singularity?
I am working on a logistic regression problem which requires minimizing a cost function J[{theta0, theta1, theta2}, X, y] to find the optimal value for fitting ...
1
vote
1answer
90 views
FindFit: getting confidence intervals for the returned parameters
I'm using FindFit[] to fit a function to some experimental data. I'd like to know what error bars are on the fitted parameters.
Scipy's ...
1
vote
1answer
135 views
Fitting parameters of user defined function returning discrete values
So, I'm fairly new to Mathematica (apologies in advance for the noobiness), and I'm having some problems regarding fitting the parameters of a user defined function to data. I'll give a representative ...
1
vote
1answer
141 views
How can I fit a matrix function with multiple variables to given eigenvalues?
I have a 5x5 matrix function H[kx]
...
1
vote
1answer
222 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 ...
1
vote
1answer
189 views
Optimizing the fitting of Ordinary Differential Equation(NDsolve) involving interpolation functions
I am a newbie to this forum. I am trying to use NDsolve to solve some ODEs involving the interpolation function. Then, I will compare the fitted curve and data to determine the ODE coefficients.
...
1
vote
1answer
53 views
How can I nicely overlay fits for multiple arrays with ListPlot or ListLogPlot?
I'm plotting multiple lists with ListPlot[] or ListLogPlot[]:
ListLogPlot[{ListA, ListB, ListC, ListD, ListE}, PlotRange -> {{0, 100}, Automatic}]
I also have ...
1
vote
0answers
79 views
Performance in parameter estimation from ParametricNDSolve using varied initial conditions
I have 250 data points from a timecourse exeriment in a list, with columns specifying (1) time, (2-4) initial conditions, (5) absorbance reading. I want to fit 4 parameters (k1, k2, k3, k4) in a DAE ...
1
vote
1answer
89 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.
...
1
vote
0answers
55 views
Fitting a set if data to a 'plane'
I have a set of data ({{1,4,2},{1,-1,2},{-1,2,4},{2,1,5},{-1,1,4},{1,1,2},{5,2,2}}) that I am some how supposed to fit to "the plane, that is with the function ...
1
vote
0answers
66 views
Method used by FindFit
Using FindFit, Mathematica selects an optimal algorithm when Automatic is selected.
I'd like to know the name of the method ...
1
vote
0answers
174 views
Methods for NonlinearModelFit
I am using NonlinearModelFit for a thesis project.
I get quite different results if I change the Method to LevenbergMarquardt or QuasiNewton or ConjugateGradient ...
1
vote
0answers
167 views
fit using parametric equations
I have experimental data with two columns (x & y). I need to fit the data to two parametric equations of the form
$$y =\text{const}_1 \times
\left( \frac{\int _a^{b}\sqrt{\frac{\left( 1+\gamma ...
1
vote
0answers
118 views
Data fitting using a model based on Eigensystem [closed]
Background (for interest/flavour): I'm writing a routine to extract certain physical parameters from a set of x-ray spectroscopy data. There are 7 parameters to be fitted; 3 (Dq, Dsigma, Dtau) relate ...
0
votes
3answers
273 views
Creating simple procedure for The Least-Square $m^\text{th}$ Degree Polynomials
I am CS major, taking Computational Numerical Analysis course. Instructor gave us freedom of choice, we were allowed to use anything or any computer language we picked, I picked Mathematica.This is my ...
0
votes
3answers
223 views
Fit line similar to power of trendline in Excel
Is there a way to fit a line similar to power trendline in Excel?
Something in this fashion: Fit[data, {1, x, x^(-n)}, x]
...
0
votes
1answer
97 views
Problem using NDSolve
This might be some simple mistake, but I am running out of ideas.
I am trying to fit an ODE system to some data. This error keeps appearing
NDSolve::nlnum: "The function value {0.299812 - ...
0
votes
1answer
48 views
Using NonlinearModelFit to fit data with errors
Assume we have some data of measurements
SeedRandom[9];
data = Table[{i,2*(1 + 5*RandomReal[])*Exp[-0.01*(1 + RandomReal[])*i]}, {i, {0, 100, 200, 400, 700}}];
...
0
votes
1answer
176 views
Problem with NIntegrate in NonlinearModelFit
We are receiving many error messages when using NIntegrate with NonlinearModelFit. Here is a much-simplified version of the code. It arrives at the correct answer after several messages saying that it ...
0
votes
1answer
111 views
System Identification with large Input/Output Data
I have some questions about system identification.
I made some measurement of current step (input) and voltage response(output) and I want to fine the parameters of my impedance.
The sample rate is ...
0
votes
0answers
70 views
FindFit and NIntegrate with dependency between integration variables
I am trying to use FindFit and NIntegrate in this situation:
...
0
votes
0answers
130 views
Fitting a theoretical density function with log-return sample
I am working on a exercise to fit a theoretical density
function,presented below, with log-return series of a stock.
$\frac{1}{2}a e^{a(x-\mu)} \quad \text{if x } < \mu $
or
$ ...
0
votes
0answers
156 views
NonlinearModelFit and NMinimize [closed]
I'm doing a non-linear fit on some data. The calculation residual is low, but I prefer to minimize another objective function such as:
...
0
votes
0answers
88 views
NMinimize::nnum: Question for fitting the data
I'm just wondering if someone could help me solve NMinimize::nnum: problem? I still can't find a solution for it. I used NDSolve to solve my functions. And trying ...
0
votes
0answers
126 views
FindFit for an implicit function [closed]
Is FindRoot generally employed in the function definition when using FindFit on an implicit function (as in an example given in ...
0
votes
0answers
180 views
ParametricNDSolveValue or NDSolve + fitting
I have been trying to find the value for the parameter kestim that yields the best fit of a model to some data points. datac has ...
0
votes
0answers
153 views
NonlinearModelFit:cvmit: Failed to converge to the requested accuracy or Precision within 1000 iterations
I am trying to find some parameters from a model using NonlinearModelFit, but I always get the same error:
NonlinearModelFit:cvmit: Failed to converge to the ...
0
votes
0answers
251 views
Find parameters to fit data with a function
I have a question regarding to find parameters (k1 & k2) to fit functions. At the beginning, I guessed ...
0
votes
0answers
236 views
Gaussian processes for machine learning [closed]
What solutions are there for Gaussian process regression and classification in Mathematica? Examples are gratefully received.
-1
votes
1answer
57 views
FindFit and Integration errors
First off, appologies for what may sound like a newbie question, as I am very new to using Mathematica.
I am trying to find a way to get Mathematica to give me an expression that would describe the ...
-1
votes
1answer
177 views
Multivariate Function Approximation With a Large Dataset
I have a nice amount of data from a trading strategy I am working on, where I have two different liquidity parameters as x, y variables.
Before entering a trade I am taking the moving average of ...
