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

learn more… | top users | synonyms (1)

6
votes
1answer
468 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 ...
5
votes
3answers
327 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 ...
5
votes
2answers
2k views

In finding a logarithmic fit for some data (of the form a*Log[b*x]), WolframAlpha succeeds where Mathematica 7.0 fails, why?

I would like to fit a function of the form: $a \log(b x)$ to a set of data: ...
4
votes
0answers
203 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 ...
4
votes
2answers
472 views

Linear regression in a chosen range of points

Hi I'm absolutely newbie in Mathematica and have following problem: My list looks like {{50, 0.75}, {51, 0.76}, ..., and I want to choose a range out of my ...
6
votes
2answers
206 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 ...
6
votes
2answers
561 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 ...
6
votes
1answer
416 views

Mathematica vs Sigmaplot (Non LinearModelFit)

I asked a question in a previous post that was closed because "The title of the question is not correct and the issue here is too trivial to help anyone later". NonLinearModelFit It's possible ...
5
votes
3answers
200 views

Looking for ideas for handling a complicated fitting problem

I have the following data: ...
5
votes
2answers
579 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: ...
4
votes
1answer
243 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 ...
3
votes
1answer
119 views

Troubles with FindFit for ODE

I need to use FindFit for ODE with arbitary number of parameters. This code (from documentation) works: ...
3
votes
3answers
225 views

Plot least squares curve on Linear Log Plot

I have the following Data: ...
3
votes
3answers
286 views
3
votes
2answers
310 views

How do I find the best fit?

I am trying to solve following system of three differential equations ...
3
votes
0answers
308 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
2answers
99 views

FindFit working with Integrate but not NIntegrate - I am using “?NumericQ”

I'm having some syntax problems with finding a fit to an equation that doesn't have an analytical expression for it's integral. Because I think the problem is one of syntax, I am substituting a ...
2
votes
0answers
140 views

Power::infy: error using FindFit [closed]

I have a 2D data to fit (the Airy type pattern from diffraction of Gaussian beam on the circular aperture). Please see the attached picture. I was going to use a function like ...
2
votes
2answers
888 views

Line of best fit on LogLog plot

I have a LogLog plot, and i'm unsure about how to fit a line to it. The data represents a calibration curve. ...
2
votes
1answer
2k views

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

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

making a function of fit results

I have 13*25 datasets consisting each of around 40 points. They are all linear I can easily fit them using fit function but my problem is when I want to call them I want them to be functions. I want ...
2
votes
1answer
508 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
71 views

Simultaneous fitting to multiple data sets with multiple variables and some common parameters [duplicate]

I am trying to fit two data sets to a function model described below which share a few common parameters. Say I have two functions with some common parameter(s) ...
1
vote
1answer
58 views

Why does my Dynamic NonliearModelFit keep running?

I have complex data and which I am fitting to a complex formula. In order to use NonlinearModelFit I split the formula and the data into real and imaginary parts. ...
1
vote
1answer
202 views

NonLinearFit with “complicated” integral model

I have a set of data $y_i (z_i)$ with errors $\Delta y_i$ ...
1
vote
1answer
238 views

FindFit::nrlnum What am I doing wrong?

I have a model called qobs: ...
1
vote
1answer
294 views

Can ParametricNDsolve be used for coupled PDEs with 5 parameters?

I have a system of coupled PDEs with five parameters that I only know ranges for rather than explicit values, and I was wondering if I could define a parametric equation with ParametricNDSolve and ...
1
vote
1answer
370 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 ...
1
vote
1answer
186 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
vote
1answer
1k 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 ...
1
vote
1answer
261 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
1answer
183 views

Logarithmic curve fit in data

I have the following data which are the theoretical: ...
0
votes
1answer
205 views

How do I fit NDSolve result to experimental data? [duplicate]

I have two coupled ordinary differential equations which I solve numerically in Mathematica, but now I want to fit the solution with experimental data. I do following, (the experimental data ...
0
votes
1answer
274 views

FindFit: why do I get negative value as result?

I am trying fo fit a model to data using FindFit. ...
0
votes
1answer
541 views

Fit implicit function

Can anyone help me with fitting an implicit function to data? The function is given by: a*x^2 + 2*b*x*y + c*y^2 = e under the condition ...