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

learn more… | top users | synonyms (3)

0
votes
0answers
24 views

Speed up evaluation of “ParameterErrors” from NonlinearModelFit? [on hold]

I am fitting my data to the analytic solution of a coupled differential equation with up to ten fit parameters. The fit itself takes 40 seconds however when I want to obtain the parameter errors, it ...
8
votes
3answers
121 views

smooth spline through airfoil coordinates

I am trying to produce a smooth spline curve through a set of airfoil coordinates. An example for the data I am trying to use is here, and I am reading the file like so to get rid of some extraneous ...
4
votes
0answers
59 views

Does Mathematica have built-in support for multivariate regression?

I know that LinearModelFit can generate a model of a single response variable as a function of a set in input variables. Does Mathematica provide support for ...
0
votes
1answer
33 views

Is it possible to get same answer from NonlinearModelFit with and without errors on data? - How to insert errors in NonlinearModelFit?

I want to use NonlinearModelFit with the following data. I tried it firstly without inserting any error bar. ...
3
votes
3answers
121 views

Automatically isolate the linear part of my data so that I can find its gradient?

I have some data plotted which is of bacterial growth curves, I have 96 sets of growth curves and I am wondering if there is a quick way to extract the straight line area of my growth curves in each ...
0
votes
0answers
3 views

Maximum Likelihood Approach for parameter estimation of multi response data, could you provide a tutorial? [migrated]

I was trying to fit the parameters a time dependent system coupled of ODES relate to a kinetic experiment with multi response data. example: A->B+H A+H->C+H A->D dcA(t)/dt=-k1Ca(t)-k2Ca(t)*Ch(t)-k3*Ca(...
2
votes
2answers
197 views

Curve fitting with this modified integrated log-normal function and extracting fitted?

The data to be fitted is for y vs x. We have y and x points. We do not have data for w. In fact, w variable is being varied during integration from 1e-9 to 100e-9. The fitting parameters are Ms,sigma,...
4
votes
4answers
859 views

Remove linear trend from data

I have a large data set with 150k lines and two data columns. I noticed that there is a linear trend, which I want to remove. So, I do the following: First, fit with a linear model: ...
0
votes
1answer
89 views

Importing Data to interpolation

I have an external file in extension XLS with looks as follows: This file can be obtained by the link below: Velocidade Angular With certainty this file is generating a list inappropriate for the ...
0
votes
1answer
67 views
1
vote
3answers
241 views

How to fit a Distribution to data that already looks like a distribution?

I have a set of data that is already ordered as a distribution. Here is a picture worth 999 words: I tried FindDistributionParameters, and ...
1
vote
1answer
71 views

getting a following error,large data points,desired output-best fit to expt. data sets

I am trying to carry out list operation but running into a following error I have large data sets(more than 0.2 million data points) and desired output will be a best fit (numerical data points ) to ...
3
votes
1answer
83 views

Knowing the functional form, how to find best-fit parameters and their uncertainties for a set of raw data in Mathematica 8?

I am trying to plot the best-fit curve (with known functional form but free parameters) passing through the following set of discrete data points which would take into account the size of error bars ...
5
votes
4answers
99 views

Using Manipulate to find best starting parameters to fit data

Often, curve fitting is very sensitive to starting values of parameters. It would be great, if I could to find such starting values of parameters "by hand" using Manipulate. So, I plot in ...
0
votes
0answers
38 views

Constrain a series of parameters while using FindMinimum

I'm working on fitting some experimental data using a model function that consists of sum of Lorentzians with width parameters A[1], ...
1
vote
1answer
46 views

How to symbolically solve the minimization problem in simple linear regression

I want to use mathematica to symbolically solve the minimization problem in simple linear regression: $${\text{Find }}\text{arg}\min _{\alpha ,\,\beta }Q(\alpha ,\beta ),\qquad {\text{for }}Q(\alpha ,...
-1
votes
1answer
55 views

Constraining FindFit to a range

I'm trying to fit data, that I obtained from measurements, to a theoretical model. The way I see it, FindFit or NonlinearModelfit...
1
vote
1answer
84 views

Fitting Lorentzian Distribution to Data

I am trying to fit a Lorentzian distribution to my data, and I was trying the solution provided by blochwave in this post. The model I am using is $f(x) = \frac{a}{(\frac{b-x}{c})^{2} +1}-1$, which ...
1
vote
1answer
89 views

Multivariable non-linear fitting

I have a function called "C" that I know it depends on 6 variable. I have a set of data points, 6 rows by 9 columns, in which in each row only one variable is changing and the rest of the variables ...
3
votes
1answer
224 views

FindFit with parameters which are simultaneously in initial conditions

I have RLC circuit. I would like to find R and L by using FindFit, but L is in initial condition and I have problem with it. Could you help me ? ...
7
votes
2answers
134 views

Inflection point and curvature

Through a coordinates list and then interpolating them I got a $f[x]$. ...
1
vote
1answer
118 views

What is the source of error in the following fitting procedure in Mathematica 8.0? [closed]

I am trying to fit the following data with a user-defined model. A priori, we know that this model is supposed to be the best fit for the given data. But, I do not know why I am receiving many error ...
0
votes
2answers
54 views

Quartic function from data [closed]

I am studying something about interpolation. I have a function that is a power x function (f[x_]:=17000 x^-1.85). From this function I got a list with coordinates ...
1
vote
2answers
87 views

NonlinearModelFit with indexed parameters

I have an instrument calibration problem for a multi-channel instrument. Some of the calibration parameters are common between channels, while others are per-channel. Toy example: ...
0
votes
2answers
65 views

Get slope of linear fit

This may seem silly, but I've been crazy for the last hour trying to find a way to automate the linear fit of my data. All I need is the slope. Say I have some data ...
12
votes
2answers
3k views

What is the best distribution for my histogram?

I defined a security bound for a random walk (cube with 15 length) and I have this code to obtain a sample of the random times at which the random walk crosses the boundary for the first time: ...
0
votes
0answers
32 views

Priority on Fitparameters

I try to fit a function using the FindFit expression. My problem is that ZL has to be ...
1
vote
1answer
58 views

Surface fitting involving factorial function [closed]

I have a large data set made up of triples, (x, y, f(x,y)), x, y and f(x,y) are all integers. I don't know the function f(x, y) and my goal is to find (estimate) it. I do know that x can be any ...
3
votes
3answers
149 views

Simultaneous plotting

For my experiment, I have to simultaneously fit the real part and imaginary part of cavity reflection data which is given here column 1: frequency, column 2: reflection magnitude, column 3: phase I ...
0
votes
1answer
39 views

Interpolating data while imposing the behavior of a cumulative distribution function

I would like to interpolate a data set which represents a curve of an empirical cumulative distribution function (CDF). Hence, the y entries are between 0 and 1, continuous and non-decreasing, and at ...
1
vote
0answers
68 views

polar form of generalized superellipse (not Gielis formula!)

I am looking for the polar form of the following generalized superelliptic shape such that I can use it with NonLinearModelFit for curve fitting to data: $$ \left |...
1
vote
1answer
74 views

Predicting the initial conditions of orbits inside a closed curve

I have a data file containing the four orbital element $(x,y,p_x,p_y)$ of a two-dimensional closed loop orbit. Note that the exact implicit equation of the orbit is not known. The plot of the 2D ...
5
votes
0answers
87 views

Softmax Regression Classification Algorithm

I'm following the Stanford Machine Learning course while simultaneously developing my Mathematica abilities. I'm having issues with my Softmax Classifier implementation (for ref, have a look at these ...
1
vote
2answers
107 views

Complex Fit, using NMinimize?

I'm having trouble fitting this complex data: ...
0
votes
1answer
37 views

NonlinearModelFit error: the function value is not a list of real numbers with dimensions {101} at {a,k,m0} = \ {1.,1.,1.} [closed]

So I'm trying to find a sigmoidal fit for my numerical solutions of these two ODEs but I keep getting an error and I don't know how to get around it. Here's my code: ...
14
votes
2answers
652 views

Fit a function to data so that fit is always equal or less than the data

I have a set of measurement data and I try to fit there a function (a Exp[b x] + c Exp[d x] - o). I have two problems: The fit function does not converge nor ...
0
votes
1answer
88 views

Data Fitting problem

I'm having this kind of data, and I know what possibly the equation is, i suspect this has a sine equation but the plot not really seems sinusoid. so what possibly the equation is so i can do the ...
2
votes
2answers
123 views

Nonlinear Fit sometimes does a good job and sometimes doesn't

So I'm trying to fit data, for all my data, the same fitting function can be used. Sometimes the fits actually FIT really well. Sometimes they just look completely random. Here's an example of it ...
0
votes
0answers
61 views

Solve equations involving summation expressions in Mathematica

I am trying to solve the simple linear regression equation analytically in Mathematica (not using builtin functions). I managed to calculate the gradient as follows f is loss function using RSS and ...
0
votes
1answer
53 views

Using LinearModelFit, how can I test the hypothesis $\beta=c$ with $c\neq 0$?

Assuming a simple linear model $y=x\beta+u$, is there a way to test the hypothesis $\beta=c$ with $c\neq 0$, using the LinearModelFit?
0
votes
1answer
75 views

FindFit works, NonlinearModelFit doesn't

I have a problem using NonlinearModelFit vs FindFit. Here is my code. ...
-2
votes
1answer
123 views
0
votes
2answers
65 views

Fitting log-linear data

I am using NonlinearModelFit to extract the gradient of what appears to be linear data in a logplot: ...
20
votes
3answers
3k views

Fitting fractional complex data with NonlinearModelfit

I've difficulites with the NonlinearModelFit function. In principle Mathematica should be able to deal with complex data. E.g. if I define the following table <...
0
votes
0answers
29 views

data fit using second order PDE

I'm trying to find the parameter for second order PDE using data. i don't know what is the error of that, ...
1
vote
2answers
84 views

How to calculate unknown parameters

I have measurement data from impact test-test specimen location (Charpy). I am used by the plotting in excel this formula hyperbolical tan Y=y0+a*tanh[(t-x0)/b] ...