Tagged Questions

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

100 views

LinearModelFit: Standard error or Standard error of the mean on the slope [closed]

UPDATED 02/14/16 Let me make this question clearer. Suppose each measurement that I make consists of three points, each with its own error governed by a normal distribution, on an XY plot. Obviously ...
117 views

LinearModelFit: How to compute R-squared? [closed]

Is there a simple way to computed the R-Squared(adjusted and not adjusted), from the LinearModelFit? It has so many options, but none for the R-Squared, that I suspect there's a simple way to compute ...
87 views

Fitting bivariate data using FindFit [closed]

I am trying to fit the following bivariate data set using the FindFit function: ...
67 views

Problem with FindFit: Low quality of estimated parameters

I'm trying to fit a Cole-Davidson formula: ...
186 views

Linear fit with conditional noise distribution

I need to fit a linear model of the form $y_i = a · x_i + b + e_i$. The $e_i$ are independent noise from a distribution that depends on $x$ as well as on global parameters of the data; however, the ...
133 views

Find a family of curves

I have a diagram with seven curves (each with a different parameter). My goal is to find a function for the family of curves (i.e. a single function not just for the seven parameters, but for all ...
81 views

How can I calculate the root of any order of power series

How can I calculate the root of any order of power series with Mathematica. Here I insert every quantity by hand. But I want to give a, ...
83 views

x and y axis nonlinear error fit possible? [duplicate]

I have a set of datapoints with x (position) errors as well as y (measurement) errors. Is there a way in Mathematica to fit a nonlinear function through this points, with weighting both, the x and y ...
839 views

Exponential fitting - isn't actually a BUG there?

There are many questions on this site about wrong exponential fitting in Mathematica but no one considers this well-known problem as a potential bug. Usually people suggest well-known workarounds ...
331 views

Findfit does not find the best fit

I am working on a project that needs curve fitting. The experimental data should be fitted with a model that calculated with an integration equation. At first, I enter my experimental data ...
96 views

How to fit parameters, not functions?

Given a set of parameters ...
74 views

How to realize Global Fitting with shared parameters, same as OriginPro9.0? [closed]

I have an experimental data from Michelson interference and I can fit the envelope in OriginPro9.0 using Global Fitting with shared parameters. The figure by OriginPro9.0 is like this: However, I ...
76 views

Paramter Scans and $\chi^2$ Test in Mathematica

Is there any in-built function or a recommended package that enables one to find, say, 10 Parameters, which are used as boundary conditions in NDSolve, that minimize $\chi^2$? ...
504 views

Fitting a curve to an image object: not a superellipse, not an egg curve.. what else?

I'm facing the problem of quantifying the morphology of objects with such a shape (nannoconids... they are fossils). One of the final goals is to produce a solid of revolution and compute volume/...
104 views

Getting image data values with coordinates in circular region

I have a number of gray level images (600, with size: 2400x2400 pixel, small instance see above). In this image there is a circular region of interest. The aim is to fit a function to the gray value ...
82 views

Fitting data in Log-Log scale

I want to fit my data from a txt file to a curve in log-log scale. What I tried to do was this: ...
99 views

Fitting data with unique variable per measurement

Imagine we are in the following situation, we have a nonlinear system of functions $f$ with coördinates $x_i$, and unknown parameters $\delta_i$'s and $t$. Let this system be defined as, \begin{...
35 views

How to calculate a required definition only once for each iteration of NonlinearModelFit [on hold]

This is my first post here. I've been using Mathematica for about 4 years now to analyze data, but am still very new and have no background in formal programming. This is the first question I couldn't ...
96 views

How to improve the nonlinear fit to a data set [closed]

Some data to begin with ...
60 views

Multivariate FindFormula? [closed]

I am using Mathematica Online and want to do FindFormula with two independent variables, but I cannot figure out if it's possible and if so what the syntax is. Here's my dataset: ...
85 views

Find the linear combination of two functions to fit to a third

I have been trying to solve a simple enough problem, but I can't seem to find the proper method. The problem is given as, Find 0 < x < 1 for which, h(t) $\approx$ (1-x) f(t)+x g(t), where is ...
85 views

Fitting with constraints including the independent variable

I would like to write the following statement: data2fit = NonlinearModelFit[data2, {a Sqrt[b x + c] + d, b x + c > 0}, {a, b, c, d}, {x}] However, it returns ...
190 views

How to fit data to a convolution equation

How to fit data to a convolution equation: ...
235 views

Multiple regression curve fitting

I've got some data with 2 independent variables and 1 dependent variable I'm trying to fit a curve to. I'm really kind of a dummy with Mathematica except for the most basic things, so I looked ...
82 views

114 views

Why is TimeSeriesForecast linear?

When I use FinancialData with TimeSeriesForecast, the resulting graph is always linear and thus not very accurate. ...
95 views

FindFit and log norm function

I'm trying to fit a function to data using FindFit, but I can't find a way to replace norm function RMSE with a RMSE in log space: ...
94 views

Fitting real and imaginary parts of a function

I have an analytic form of a function G[w_] = -I*z0*w/(1 + I*z0*w*a) I know this function can be obtained (up to some overall normalization) from solving a ...
217 views

Fitting does not work

I have a set of points, which is basically one minus a Lorentz curve. And the NonlinearModelFit ...
98 views

Fitting a set of functions using same basis functions

I am trying to fit the functions in the plot below, but I need them to be fitted using the same basis functions. I want to interpolate between the functions by interpolating between their coefficients,...
82 views

Boundary parameter in Beta Distribution

I use EasyFit to find the probability distribution of my data. It turns out the data follows BetaDistribution with 0.54022,0.70601 shape parameters and 1.33,6.83 continuous boundary parameters I am ...
53 views

Displacement around the x axis, how to change a function location

While plotting a function I want to change the location of x. I am doing a regression with the logistic function ...
81 views

Data fitted by two linear fits [duplicate]

can anybody help me please and tell me how to fit my set of points by two linear fits? It is always exactly two of them and are always linear and should cover all the data. The second line should ...
71 views

problems of Lorentizan fit with Nonlinear fit model [closed]

I tried to do a Lorentzian fit for a Spectroscopy data.I found that I have to actually give the precise value for this fit.[i do not like to call this as fit ,if that is the case]? Am I missing ...
88 views

What´s wrong with my FindFit

I updated the data which is a table I deleted the first coordinate as it was the quote from the document. ...
79 views

Invert and fit implicitly defined curve

I need to fit an implicitly defined curve. I thought I could get some data out of Solve, and then using FindFit. Therefore, I ...
99 views

Fitting in Mathematica: Which function? [closed]

in other programs, there is a possibility to take a data set and to find the function which fits best. Is there also such a possibility in Mathematica? I only could find ...
98 views

NonlinearModelFit gives imaginary numbers [duplicate]

I am having trouble using NonlinearModelFit to fit to data generated by the equation I am trying to fit to. ...
96 views

Is there a built-in function implementing the minimum and maximum gradient?

Suppose I have a set of data. Mathematica has fitting functions to determine the line and corresponding equation to the best fit given any arbitrary set of data. But in experimental techniques, ...
94 views

Fitting data using ParametricNDSolveValue and NonlinearModelFit [closed]

I'm trying to evaluate the kinetics of the chemical reaction. For that I need to fit my experimental data to the kinetic equation. These are my steps in Mathematica. ...
73 views

Detecting and measuring an ellipse in a glaucoma photo? [duplicate]

I've tried the solutions given in How to find a circular object in the image glaucoma? to detect the ellipse, but the detection results are not quite what I wanted. In glaucoma we have a cup to disk ...
1k views

Detecting an ellipse in a glaucoma photo

For glaucoma diagnosis it is common to determine a "cup to disk ratio" which compares the diameter of the optic disk (VDD) and optic cup (VCD). The optical disk is visible as a circular red feature (...
161 views

Fitting to the system of equations with no analytical solution

I'm trying to fit linear combination of 2 functions to my experimental data set (it represents voltage of 2 photodiodes - Voc1 and Voc2 - connected in series under illumination - S) ...