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

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2answers
112 views

Error function fit of data

I have this experimental data set which I know should follow the Complementary error function. My goal is to find the σ of the associated gaussian distribution. However, I cannot seem to do it in ...
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1answer
123 views

Discrete peaks to curve via Voigt summation

I have two data sets. One is an experimental recording of an absorption spectrum, composed of regularly spaced (wavenumber, intensity) coordinates with a fine wavenumber resolution, thus making ...
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2answers
142 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
122 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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1answer
67 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 ...
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1answer
83 views

Find polynomial equation for set of 3D data

data was given in columns in the order {y, x, z}, with y dependent on x, z ...
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1answer
130 views

Fitting to a sigmoidal model

I am trying to fit a set of stochastic data to a sigmoidal function, but it's not working. Can you please help? Here is the function I am trying to fit to my data. ...
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1answer
121 views

Nonlinear fit with piecewise functions

I have an ensemble of data points $(x_i,y_i)$ and I need to fit them according to $y=F(a,b,x)$ if $x \leq x_{ref}$ and $y=G(c,d,x)$ if $x \geq x_{ref}$. The parameters I need to adjust are then ...
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1answer
92 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 ...
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1answer
127 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
51 views

Can I use boolean parameters in LogitModelFit?

For example, to use 1 as True and 0 as False: ...
0
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1answer
44 views

What is the definition of FitResiduals

What is the definition of FitResiduals in Mathematica? I could not find its definition in the Mathematica help. Is it the same as chi squared?
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1answer
63 views

Logarithmic curve fit in data

I have the following data which are the theoretical: ...
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1answer
96 views

Fitting data to a Poisson distribution

I'm trying to fit a Poisson Distribution to data produced in a lab. I've successfully made a Histogram of the data, which looks like: However, when I try to fit the Poisson Distribution using: ...
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1answer
210 views

Obtaining the envelope of an oscillating function and perform fitting

There is an elegant way to obtain the envelope of an oscillation function explained here http://mathematica.stackexchange.com/a/27854/15966 My question is how to modify the code below so I can fit ...
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1answer
185 views

Exporting tables of interpolating functions

A few weeks ago I asked a question about manipulating parameters in NDSolve (Looping with NDSolve?) , and received some very helpful advice about the manipulate environment; now I want to take the ...
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1answer
91 views

Constraining some rows from LeastSquares to lines

For two matrices, A and B, with dimensions {n,p} and ...
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2answers
154 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 ...
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1answer
198 views

Fitting a Function With a Numerical Integral [duplicate]

I am having trouble using FindFit with the following function. ...
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1answer
216 views

FindFit: why do I get negative value as result?

I am trying fo fit a model to data using FindFit. ...
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2answers
186 views
0
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1answer
386 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 ...
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1answer
87 views

Solving one equation, then inputting the values into another for NonlinearModelFit

Considering the equation a*x^3 + a*x^2 + x + b == 0 I'm looking to find the best value for a and ...
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0answers
26 views

NonlinearModelFit::nrlnum error using FindFit /NonlinearModelFit

My question is related to my previous post I'm trying to fit experimental data (after suggestion here by David) with Airy type function `data01 = Import["366.0000cm_660.0000nm.png"]; data02 = ...
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0answers
74 views

Memory problem in Mathematica 10

I'm having a problem with memory. I'm doing nonliner fits of several data lists to a system of differential equations. When I evaluate the "Do" cycle the memory grows with the iteration step up to my ...
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0answers
53 views

Fit convoluted Gaussian and Lorentzian functions to a peak profile

Thanks in advance for anyone who read this. I have a peak profile data like this: ...
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1answer
60 views
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0answers
52 views

No real number fitting double exponential in Mathematica

I am trying to fit a double exponential curve to my data, but I got the error saying there are non real number. Also I tried with starting values for my 4 parameters, but this does not work either. ...
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0answers
55 views

Horizontal shift in fitting data by a sinusoidal nonlinear model

I have data that can apparently be fitted by a sinusoidal function in form $D+A\sin(B(x-\frac CB))$. I tried doing the best fit in Mathematica using ...
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0answers
38 views

How do I constrain the result of fitting my non-linear model to be greater then 0

fitresulty21 = NonlinearModelFit[ydata21, {funfit[y, σ, A, B, x1, d, d/2], A > 0}, {{x1, 20}, {σ, 3}, {A, 200}, {B, 2000}, {d, 110}}, y]; ...
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0answers
32 views

Fix Parameters for NonLinearModelFit?

Is it possible to fix the parameters for NonLinearModelFit within the function itself instead of defining the fix parameters at the beginning of the notebook? I am ...
0
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1answer
84 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 ...
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0answers
32 views

Data Fitting with xerrors and yerrors using findfit [duplicate]

I'm trying to fit data with xerror and yerror using "Findfit", so i'm trying the same form than in tuto : ...
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0answers
35 views

Fitting for multiple data in Mathematica [duplicate]

I've just started to use Mathematica for programming and I was wondering how I could do Fitting for several data sets. For example, I have one curve. For this curve I need to plot a fit curve, if my ...
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0answers
42 views

How to approximate a computationally expensive 5-dimensional manifold?

I have a 4-parameter family of functions, which I'll refer to as y[a, b, c, d][x]. In this notation, a, b, c, d are the 4 ...
0
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1answer
69 views

Trouble fitting an explicitly complex model with the TransformedFit package

This is follow up from a previous question in which @Oleksandr R. suggested the use of a package he developed for splitting a model and data into real and imaginary parts to avoid a problem with ...
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0answers
43 views

Fitting data involving units

I want to fit some data to a model. However, if the data involves units in the independent variable, fitting seems not to work. As an example, consider the code ...
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0answers
49 views

fitting system of ODEs - “part2 of {} does not exist” errod

I'm trying to fit my data to a system of ODEs: x'[t]==a*x[t]+b*y[t] y'[t]==c*y[t]+d*x[t]+e*z[t] z'[t]==f*z[t]+g*y[t] having t,x[t],y[t],z[t]. I followed the code ...
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0answers
76 views

Speeding up Nonlinearmodelfit by constraining parameters?

I have a complicated parametric PDE that can be fitted to some data with NonlinearModelFit, but takes several hours to estimate the best values of the four free parameters. Currently, the code ...
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0answers
70 views

Simultaneously fitting data sets with many variables as free parameters

I found a partial answer in the documentation centre, but would like to expand on it and know how can I fit multiple sets of data and extract the parameters from them. It is an eigenvalue problem - We ...
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0answers
196 views

histogram fit for probability density

I am trying to fit the (probability density) histogram of some data with the exponential function, but I am having difficulties. My raw data are in file called ...
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0answers
41 views

Supply parameter values in NormFunction of FindFit

As I understand the input to the NormFunction is a list of residuals. Is there a way to get parameter values into the NormFunction as well? I ran into a problem where the norm depends on the values of ...
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0answers
73 views

Find Numerical Derivatives (With Errors) given some data

I have a question. Suposse I have some data with their respective errors: ...
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0answers
177 views

Non linear model fit mathematica

I want to fit experimental data (temp,alpha) to the following equation for calculating k and Ea -Log[alpha]^n = function(k,Ea,temp) However i do not know ...
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0answers
131 views

NonlinearModelFit with multiple parameters

I am now trying a slightly more complicated model which actually consists of finding the parameters of 2 particles in an Image (I attached an Plot of an image). Although I put very good initial values ...
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0answers
66 views

Fitting data set with series expansion

I have a function given in a form of a list: ScalarField={{$\epsilon$,$y_1$},..{1,$y_{3000}$}} It is defined in the range $(\epsilon,1)$ (spacing between grid points is homogeneous), where ...
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0answers
111 views

Using FindFit for step functions

Having used FindFit like so: ...
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0answers
100 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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0answers
125 views

How could I code the following nonlinear regression?

I am an extremely limited user of Mathematica. Could someone tell me how to set the following nonlinear regression problem : Y = Sum[a[i] F[i,X] , i = 1,4] ...
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0answers
41 views

How to fit ODE's coefficient, just like using NMinimize [duplicate]

I want to fit ODE's coefficients to a model. I tried using NMinimize, but it seems it does symbolic instead of numerical calculations. ...