Methods used to fit curves (as in linear or non-linear regression) to data.

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How to fit a curve for a histogram [on hold]

I am trying to fit a curve (gaussian) for my distribution represented here with an histogram, like the red curve represented in the attached shema. X = rchisq(1000, df = 5) hist(X) Thank you
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How to fit a path through a dynamic, 3D point cloud?

I have a cable I am dropping from moving vehicle onto the ground. Using a camera system I estimate the location where the rope touches the ground in realtime. Movement of the vehicle and inaccuracy in ...
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6 views

Compare R Square values of different curve fitting

I have four independent samples (e.g. time vs. weight). I have used to two different methods to curve fit each sample: 1). log transforming weight (linear-log) and fit with linear regression; and 2). ...
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28 views

Linear Regression to detect between a linear and non-linear trend

I have measured the area of spread of a number of plants through time. I'm interested in trying to ascertain whether a linear or a non-linear relationship (i.e. quadratic) best represents the increase ...
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28 views

Curve : should I use the mean or all values?

In my experiments, I measure glycemiae at 7 different times to then draw a curve with R or Excel. For more precision, I duplicate my measures, so for each time I have 2 glycemiae. For now, curves ...
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32 views

Useful references to learn the essentials of curve fitting and its application?

I know this question might be a bit too broad, but I am looking for some pointers for self-study. I am given a set of data for which I have to identify the trends, and potentially come up with some ...
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8 views

Best-fit plane for a set of points

I have a set of 3D points, ie: $P\{(x_1, y_1, z_1), ..., (x_N, y_N, z_N)\}$. Each point in the set is a stellar object, and the $(x,y,z)$ system is defined from their equatorial coordinates and ...
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38 views

How to determine when the difference between two goodness of fit values is significant?

I have a data series that I'm trying to fit to a model. I'm trying several types of models (exponential, linear, logarithmic). In order to assess which one it fits best, I use a Residual Sum of ...
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25 views

Calculate Confidence (Error) Bands for Chi Square fit with errors using Iminuit

I want to fit some data with errors to a polynomial, say $y(x)=a+bx$. I made a $\chi^2$-fit using Iminuit but now I want to calculate the error bands ( 68,3% Confidence Bands). What is the fastest way ...
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351 views

What type of regression will improve the prediction for these data?

I'm quite new to regression problems in general. I have a simple data with 1 feature. I am trying to fit a regression model so that I can predict on new data set. So far, I tried to fit a linear ...
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27 views

How to improve the model of a fit to a sinus modulated sinus

I am trying to determine the amplitude of a sinus modulated sinus as accurate as possible. My sampling frequency is sufficently high and I am currently using a LSQ fit. The entire model looks as ...
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Anscombe-like datasets with the same box and whiskers plot (mean/std/median/MAD/min/max)

EDIT: As this question has been inflated, a summary: finding different meaningful and interpretable datasets with the same mixed statistics (mean, median, midrange and their associated dispersions, ...
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10 views

combining two linear fits

I have two linear fits, in this case taken from two calibrations of an instrument, one before and one after a field project. For the two linear fits I have the covariance matrix, but not the original ...
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12 views

How to find deviations in a signal?

I have a sinusoidal wave data with a noise in it. I know the details of the sinusoidal wave (Amplitude, frequency, Phase, bias). I am trying to find out the exact time and the duration for which the ...
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34 views

Curve shape estimation based on reference curves [closed]

I have a set of exponential curves $ ae^{bx} $ that represent the speed-power curve for a given vehicle (for a specific speed you need to use y amount of power). And given a point $ (speed, power) $ ...
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19 views

How does a curve fit accuracy depend on the number of points?

The accuracy of a curve fit must increase with the number of points (perhaps like sqrt(N)), but I haven't found an equation for it. Trying estimate accuracy of a 2nd order poly fit. Thanks.
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26 views

Averaging Cumulative Distribution Function

I have several (x,y) datasets which form various CDF curves. These are generated by cross-validating models built with different parameters. For example: ...
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21 views

How to modify a curve so that it reference another curve

Let's say we have a curve A with 50 time points (max = 60, min = 1). One way I can do is to standardize the values of the curve and make the range become [0,1] instead of [1,60]. However, I have ...
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108 views

how to fit pdf of known form to data

I have a set $X$ of 1000 data points. I know the PDF has a certain form, but there are two constant parameters for which I need to derive values in order to bet fit the data. Is there an established ...
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142 views

What does negative R-squared mean?

Let's say I have some data, and then I fit the data with a model (a non-linear regression). Then I calculate the R-squared ($R^2$). When R-squared is negative, what does that mean? Does that mean my ...
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30 views

Curve fitting - accounting for variability caused by different initial conditions (Matlab)

I'd like to fit a Gaussian model (composed of 1 to 5 Gaussians) to 55 data points, and then repeat this process for >1000 more data sets, each having 55 data points. I'm interested in the fitted ...
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8 views

Compare two groups fitted with different models

I have two group means that "behave" in different ways. Group A increases and reaches a "plateau-like" value. Group B stays almost steady. I have used a polinomic fit (cubic) for group A and linear ...
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101 views

What do I fit to a heavily positively skewed histogram?

I have a data which has heavily positively skewed variables. My manager has told me to fit it some distributions (univariate). The problem is that for most of the data the mean is far closer to the ...
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12 views

Curve fitting and analytical solutions vs kernel density estimation and sampling

I have some data, and I want to find the expected value of the maximum of $n$ samples of this data. What of the following methods would typically get me the best results? Visually inspect the ...
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63 views

How to estimate a probability distribution

Suppose I want to estimate a probability distribution, is it common practice to simply fit a function to a frequency histogram? So in my work, I am training a classifier, the performance of which is ...
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16 views

What function fits these criteria?

I want to use a function $f(x)$ to model my data $x$, where $x > 0$, and then fit the function's parameters to that data. My requirements are that $f(x)$ is continuous and smooth, $f(0) = 0$, $f(x) ...
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117 views

Fitting data to multimodal distributions with scipy, matplotlib

I have a dataset that I would like to fit to a known probability distribution. The intention is to use the fitted PDF in a data generator - such that I can sample data from the known (fitted) PDF. ...
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11 views

Fitting function to unreliable data - simultaneous optimization of parameters and observations

I try to fit noisy (biophysical) data. The data are expected to fit a relatively simple, two parameter function. My measurement is flawed in a way that introduces systematic errors to my data. I ...
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130 views

Simple Log regression model in R

I am trying to fit a regression model, as the plot says the relation is log. I tried to use lm(logData$x ~ logData$b3, data = logData) but it did not work ...
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40 views

How do I estimate a smooth cdf from a set of observations?

I have a set of observation, let's call it $X$ and would like to fit a cdf to it. $X$ has a distribution which is roughly approximable with the normal distribution. This CDF should correspond to a ...
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19 views

Creating data to fit some curves

I am not a statistician and I am not expert in R, but I know to use some codes. I need to plot some curves which I got their R codes to plot, but I need to create the data (samples) for some simple ...
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Why are the basis functions for natural cubic splines expressed as they are? (ESL)

I'm doing some self-study with ESL (http://www-stat.stanford.edu/~tibs/ElemStatLearn/download.html) and I've come to 5.2.1, the section on natural cubic smoothing splines and I'm having conceptual ...
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Select a fittting model for histograms varying the number of Gaussians

I have many data in the form of one dimensional histogram, to give an example consider the data at http://pastebin.com/embed_js.php?i=1mNRuEHZ I expect that these data are obtained from a pdf ...
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23 views

Why fitting does not find the true best point

I fitting an expression of the form: $s(t)=\frac{1}{1+\exp[a+\sum_k b_k x_k(t)]}$ Where $a$ and $b_k$ are fitting parameters and $x_k(t)$ an input time series. I have $k=1,...,N$ different types of ...
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308 views

Fitting known equation to data

I have measured growth rates over a range of temperatures (temperature response curve) and would like to fit an already established equation/model to it. I'm very new to R and have trouble coding it ...
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120 views

Fluctuations in hazard function at high (x) values

Using a best-fit algorithm, i've obtained gamma-distribution parameter MLEs for my data (scale and shape). When evaluating the hazard function, calculated as the PDF divided by the reciprocal CDF, ...
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74 views

Weibull fitting

I'm trying to fit a Weibull curve to my xy data. I know that the 3 Weibull model has 3 parameters, the scale, the shape and the location and I would like to estimate them from my data. I used curve ...
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63 views

R - fitting a gamma distribution given the CDF?

I'm trying to develop a prediction model of the success or failure of a test run based on its current running time (in my data, from observation, the longer a test runs the more likely it is to fail). ...
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28 views

plot integer data on a log-log scale

I'm new to statistics, and this may be a very trivial problem. I have an array of sorted data: ...
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15 views

Fitting to a sum (mixture?) of components

I have a curve-fitting problem in which I'm fitting my data to a sum of components with identical functional forms but different parameters. That is $d_i = f(x_i | \theta_j) + f(x_i | \phi_j) + ...
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33 views

are there anomalies? and if so, can I quantify them?

Given a data set, I want to divide it in two different sets if I see that part of the data misbehaves. For example, in the figure you can clearly see that something is happening before the vertical ...
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74 views

Nonlinear regression curve fitting doesn't work

I'm stuck with some seemingly easy task to fit nonlinear regression model. It worked normally until some new data came. Here is my code: ...
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48 views

Forecasting bank account balance data

I'm new to statistics and not even entirely sure how to frame my question properly, so please go easy with me. I would like to be able to do 2 things: Take a series of dates and bank account ...
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59 views

Why is my sinusodial fit not working well for this data?

I'm trying to find the best fit line for this data below but no matter what I try, the fit line seems to never be able to account for the lower values as shown below. The x-values are just dates from ...
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22 views

Calculating the confidence interval of a curve fitted through data points each with a confidence interval itself

I have a number of data points, (x,y), where both variables represents a measured quantity each with a confidence interval. These variables correlate strongly with each other. I want to fit a curve ...
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62 views

Best way to model this data, qfit or fpfit? How to get equation?

So I have this relationship, which is obviously not linear. The purpose is to see if there is (and what kind of) a relationship between FRAG (test score) and MD-R (mm^2/s). There are other covariates ...
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95 views

Fitting an arc from samples taken at evenly spaced angles

I have an application where I am rotating an object and measuring its position in X,Y as it rotates. There is some measurement error in both X and Y at each point (haven't yet been able to ...
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153 views

How to find (using R) the function which my experimental data follow?

I have an experimental time-depending data (Mean as a function of Time). I want to find the function which my data follow. I have already tried fitdistr and Gam, but it hasn't really helped. Could ...
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56 views

Finding the best fitted distribution for an experimental data with R

I have read most of the similar questions and answers, but still can not solve my problem... I have an experimental medical time-depending data, which I want to analyse and classify. I'm trying to ...
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Fitting distributions to multi dimensional data

I have a set of data with losses are dependent variable. It also has 2 independent variables such as location and type of injury. For each location and injury type combination, I need to fit a ...