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Questions tagged [curve-fitting]

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

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1answer
36 views

method for predicting a curve

I have data on several curves. the data is of the form: curve_id x y and there are many x/y pairs for each curve and x is limited to some known range. overall, the curves look quite similar in ...
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0answers
18 views

Statistical Test of Model Mean and Std.Dev

I have thousands of real-world observations for the input/output of some stochastic system. I have made a mathematical model that I have strong reason to believe governs the underlying relation ...
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0answers
38 views

How do I fit a cumulative Gaussian distribution in R? [closed]

I am trying to fit a cumulative Gaussian distribution function to my data, but I'm not sure how to do this. From what I understand, the fitting process tries to find the mean and standard deviation of ...
2
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1answer
18 views

Analyse variation between distribution curves according to factors

I have a set of continuous distributions representing the leaf area density found at different heights through a forest canopy. e.g. like that found in Whitehurst et al. (2013): For each of these ...
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0answers
9 views

How AAE is calculated for curve fitting and what does it's value indicate?

I have experimental results which are fitted to different equations, the fit is assessed by R^2 and AAE and I don't know how to interpret AAE values.
1
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1answer
32 views

Finding the appropriate polynomial fit in Python

Is there a function or library in Python to automatically compute the best polynomial fit for a set of data points? I am not really interested in the ML use case of generalizing to a set of new data, ...
2
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1answer
42 views

How to run a regression analysis in python on a nonlinear, strange dataset

I can't figure out what type of regression analysis or extrapolation technique to use in order to come up with an equation for the data I have plotted. For a school project, I've been testing diodes ...
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0answers
9 views

Definition of a 'design adaptive' fit?

When studying non-parametric regression, I've been told that local linear fitting is often better than local constant fitting at the job of estimating regression functions because local linear fitting ...
1
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1answer
53 views

What method can I use to produce a single curve from a number of curves?

I am looking for a good method to combine a set of curves into a single curve. Those curves have been produced by performing a measurement/testing n-number of times under similar conditions. What I ...
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0answers
33 views

model of two gaussion curves

How can I create in R a model that contains two Gaussian curves that describe that data I got. So I could get in the end the sigma and median of the Gaussian and calculate which datapoint belongs to ...
2
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1answer
28 views

Normalize Weights in fitting a curve

I am trying to fit a curve to set of data points. I have a set of weights that I want to assign each point while fitting. My question is that should i normalize the weights or use the weights as they ...
1
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2answers
33 views

Define prediction interval for a monthly sales pattern

The point of my analysis is to develop an alert system to detect when the sales of the current month are deviating significantly from the monthly forecast and guess whether the month is going to close ...
1
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1answer
43 views

Curve fitting in the presence of prior beliefs about the relationship between x and y

In the figure which follows each dot represents a game of a particular sport. The x-axis represents the home team's margin of victory, and so around the top-right we can see a game where a home team ...
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0answers
54 views

What error analysis was used here?

I have two curves: one is experimental and another is fitted to the first one, the error estimation for the goodness of fit was conducted by another person 10 years ago on those data, there was two ...
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0answers
38 views

Fitting a logistic growth curve with an iterative formula in R

I'm trying to fit a logistic growth curve to specific countries GDP data using an equation, $P_{n+1} = rP_n(1-\frac {P_n}{k})$. (1) I've found constants $r$ and $k$ simply by finding a ...
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0answers
18 views

how to fit a curve on 20 pairs data [closed]

how to fit a curve on 20 pairs data ? (For instance a 4th polynomial to 20pairs datapoint) in python? And then how to add some deviation to them? for instance 0.5 deviation?
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1answer
56 views

Fitting a left-skewed curve to data [closed]

I have the following data for x and y-axis inputs. I am trying to fit a left skewed curve (i.e. long right tail) with a steep right peak to this data in R. I am not sure what curve equation to use (...
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0answers
16 views

comparing discrete and continuous measure performances

I am trying to estimate the value of the response/dependent variable based on the Age value. First, we used the defined age intervals to estimate the dependent variable and then we considered age as a ...
0
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1answer
68 views

How does Excel interpolate / imputate missing values in time-series when fitting a line to a plot?

I have a scatter plot in Excel (upper part of the screenshot) of time-series data. In-between the values that I plot (to the left), are some missings. I fit a (linear) line to those values and display ...
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0answers
41 views

Average of two fits vs fit of a combined data

Lets say I have data from two independent simulations. One of them look like this: The fitted curve is done by minimizing absolute difference between each data point and the curve. The fit ...
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0answers
17 views

Curve fitting testing basics questions

I'm learning all this stuff, so bear with me. A marketing professor in a university class, did the following: He wanted to do a projection from a very small data set of just 7 numbers. Using Excel ...
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1answer
55 views

What are some left skewed models for curve fitting?

I am working on some data on thermal performances on my organism for my thesis. I came across the Ricker Model which is a right skewed curve as shown below. How can I modify it to become a left ...
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0answers
21 views

Production Curves for Agriculture

The idea here is to fit a curve to production data in agriculture. By a production curve I mean for example the output of a mine over time, peak oil production or the yield of a farm over time within ...
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1answer
30 views

cluster analysis in R

This is (a piece of) my data frame ...
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0answers
34 views

How can I find the k-nearest neighbors for a collection of linear time series data?

I need to figure out how to determine the nearest neighbors of an "optimal" line, as illustrated in a simplified figure, linked below. The blue, orange, green, and purple lines represent the best fit ...
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1answer
251 views

How to know if a parameter is statistically significant in a “curve_fit” estimation? [closed]

I use curve_fit from scipy to estimate parameter values from a specific function. ...
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0answers
70 views

Fitting Data to an Unknown Distribution

Consider a sample $x_1,\ldots,x_n \sim F$ from an unknown parametric distribution where $F$ is the cumulative distribution. We observe data in the form $F(x_1),\ldots,F(x_n)$. Stated differently, we ...
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0answers
130 views

Fitting a Multiple Gaussian Peaks to a Smooth Curve to Calculate Resolution in R

I used interpolation to fit a smooth curve to my data. I did this in order to visualize peak and valley regions. My goal is to calculate resolution (separation between peaks). I have peak to valley ...
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0answers
8 views

Deconvolution of 2 vectors (1 know + 1 unknown)

I am currently trying to deconvolute 2 vectors (a & b) from 1 (c). Actually, I have access to the recorded data of (a) & (c) but not (b). All are signal vs time with signal totally random. I ...
5
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1answer
65 views

How to deal with unstable estimates during curve fitting?

First of all, I understand this isn't a strictly statistical question, but I've seen other questions involving optim() here. Please feel free to suggest a better SE ...
1
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1answer
36 views

Summarizing a multi-dimensional distribution

I have an empirical distribution of observations along a number of dimensions. The dimensions are either categorical or ordinal (low frequency, equally spaced time steps from 0 to cut-off). At the ...
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2answers
46 views

Compression of 18000 curves

I have over $18000$ curves that I need to compress to save $\geq 50\%$ of space. Each curve is described by points $f(1), f(2), ..., f(96)$, each $f(x)$ is 8-bit long. The curves in compressed form ...
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0answers
69 views

How can I compute mutual information of continuous random variables from discrete samples?

I have two dependent random variables $X$ and $Y$. $X$ is a continuous random variable and $Y$ is a function of continuous random variables. I know the pdf of $X$ and have a sample from it. I only ...
3
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0answers
149 views

How to fit exponential y=A(1-exp(B*X)) function to a given data set? Especially how to determine the initial start parameters? [duplicate]

I have a data set in which $y$ is roughly related to $\log(x)$. Now I wish to fit the curve $$y=A(1-\exp(BX))$$ When I use R and the nls2 function, then I ...
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1answer
70 views

Fitting a curve OVER OR UNDER a set of points

I want to fit a curve $f(x) = mx+b$ on my data points $x_1, \ldots, x_N$ using linear regression with a single predictor. However, the cost function is not even, rather, it has different weights on ...
1
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1answer
30 views

Is there a particular recommendation of exponent to use on the cost function when trying to do curve fitting in R?

I have been doing some custom curve fits in R and I noticed that using the square of the difference between curve and data resulted in results that are very ...
2
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0answers
25 views

Estimate rotation matrix from correlation of samples on a sphere

I have a process that produces samples on a sphere. I don't know the center or radius of the sphere, and the samples are highly non-uniform -- as a somewhat example, I have 90% of them in one quadrant ...
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0answers
26 views

Formutaion of Least Squares Problem

In general, to use the method of least squares, a linear stochastic system is modeled as: \begin{equation} y = ax + \eta \end{equation} where, $y$, is an observed variable, $x$ is an input while $\...
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0answers
91 views

Algorithms, models, recommendations for regression with vector output

I really didn't want to double-post, but it wasn't clear to me which StackExchange forum to post to, and I am looking for all the help I can get with this problem. Here is basically the same question ...
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0answers
145 views

Calibration Curve v. Linear Dynamic Range [closed]

We have a piece of analytical chemistry equipment (a mass spectrometer for those who care), that has the capacity to generate a "Response value" (Area under the curve) that correlates to the amount of ...
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0answers
22 views

Standardized residual for point with 0 variance

So I was fitting a curve to some data. The data looks as follows: $E = [14.9, 22.7, 28.4, 12.5, 10.5, 14.0, 9.3, 11.5, 7.1, 22.0, 5]$ $A = [924.5, 1067.8, 1124.9, 577.0, 430.3, 880.3, 333.0, 569.3, ...
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0answers
179 views

Fitting a sinusoidal curve only with max-min values

I have a series of high-low tide values, approx. every 6h, and each one has the corresponding time. I would like to get (an estimation of) the values between each record. I was thinking I could create ...
2
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1answer
67 views

Interpretting the p-value when inverting the null hypothesis

I'm performing an analysis by fitting data points to an exponential distribution and testing the adequacy of this fit using the Kolmogorov-Smirnov test. The standard ks test null hypothesis: the data ...
1
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1answer
732 views

Multiple curve fitting python

I have this 7 quasi-lorentzian curves which are fitted to my data. and I would like to join them, to make one connected curved line. Do You have any ideas how to do this? I've read about ...
2
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0answers
30 views

How to properly analyze groups of cumulative dose-response curves in a 2x2 design?

We have data from following experiment: Animals were divided into 4 groups by combination of 2 factors (2x2 design). We then extracted 2 blood vessel rings from each animal (animal = biological ...
1
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1answer
257 views

Simultaneously curve fitting for 2 models with shared parameters in R

Hi I am trying to curve fit 2 models (Van Genuchten & Mualem) with shared parameters in r. The models are: ...
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0answers
24 views

In polynomial curve fitting, why do all values have the same error weight?

Often measured data has a percentage error. For example, a 2% error on values between 1 and 50, would mean errors between 0.02 and 1.0. Why does normal polynomial curve fitting not take this into ...
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0answers
40 views

Meaning of correlation of fitted nonlinear curve parameters

Suppose that I have a curve $y(x|\theta)$, where $\theta$ are a set of parameters. My data set is tables $y_{ij}$ and $x_{ij}$. I fit the curve for each row $i$, and obtain the set of parameters $\hat\...
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votes
1answer
1k views

Finding the slope at different points in a sigmoid curve

This is my data. x <- c(0.5,3.0,22.2,46.0,77.3,97.0,98.9,100.0) plot(x, pch = 19) I want to fit a curve through these points and then calculate the slope at ...
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0answers
28 views

Plotting chi-square against another variable

Is there a way to plot chi-square error ($\chi^2$) vs. some other variable? I'm trying to replicate plots from the following paper, Figure 1-C, more specifically: As additional information, the ...