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16 views

How to compare forecasting methods: based on ARIMA and curve fitting?

I'm making a project connected with identifying the dynamics of sales. My database concerns 26 weeks (so equally in 26 time-series observations) after launching the product. I want to make forecast ...
1
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0answers
20 views

Problems with curve fitting

I have a longitudinal dataset to which I am trying to fit the following model : $$ y_{i,j} = \frac{1}{1+a_{i} \exp(-r_{i}t_{i,j})} + \varepsilon_{i,j} \tag{1}$$ The setting : $i$ ($1 \leq i \leq ...
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0answers
27 views

Which steps have to be done before fitting logistic curve to time-series?

I want to cluster time-series concerning sales of products. In the database I have 26weeks after launching each products and units sold each week. One of the method of clustering is to cluster ...
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0answers
18 views

Skewed, humpy, left tail doesn't approach 0

Self-learning statistics by fiddling around with some modeling. Having trouble finding distributions for this data however. Defined for $x >0$ $P(0) > 0$ $P(X) \to 0$ as $X \to \infty$, (very ...
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3answers
68 views

Multi-peak Gaussian fit in R

I have a large data set composed of several "independent" data frames like this one ...
0
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0answers
23 views

Negative values in the data set

I have a set of negative values and would like to put a fitted model in R. How would I approach it? Say, I want to use Gamma distribution as a fitted curve using method of moments but the data is all ...
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1answer
31 views

Fitting logistic function with pymc

I've asked this question on stackoverflow too, but no answer yet. This seems a more appropariate place to ask this question: I'm messing around with pymc to understand it a bit better. Now I am ...
4
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1answer
45 views

How can I estimate the shape of a curve where the predictor variable is right censored interval variable?

Are there methods available to conduct interval-regression style analysis where a predictor variable is the interval variable and the outcome variable is a dichotomous variable? To give a bit of ...
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0answers
17 views

Minimum points required for fitting curve

If I need to build yield curve, n what is the minimum number of data points necessary for any interpolation method, e.g. say cubic spline or Nelson–Siegel, etc. I ma not sure if I can raise this ...
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0answers
11 views

How to calculate performance statistics of continus learning model?

I have continuous weak stationary process that I need to map on logical result value (0,1). For example I want model that in 2 ways: logistic regression native Bayes classificator I want to know ...
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0answers
12 views

Least-squares, pivoting/rotating around a reference point?

Suppose I have two datasets $y1$ and $y2$ sampled equally on $x$. I would like to bring $y2$ in register with $y1$ in a least-squares sense, and referenced to one point at $x_{ref}$ in $y1$ (i.e. the ...
1
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0answers
29 views

Deep and sparse vs. Thin and dense data collection for curve fitting?

I'm designing a toy experiment in which I'd like to model the 'attractiveness' of a credit card as a function of the interest rate it comes with: Attractiveness will be reported on a 10 point scale ...
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0answers
24 views

Minimizing the sum of squares of autocorrelation function of residuals instead of sum of squares of residuals

I am trying to fit my multi-exponential model to some experimental data and I am using a simulated annealing algorithm. My objective function has so far been the sum of squares of the residuals: ...
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0answers
29 views

Fitting a parameterized 2D distribution

I frequently deal with datasets that rely on a binary classification based on a Pulse-Shape-Distribution (PSD) discrimination value. This is based on a 2d fit of the PSD value vs the amplitude of the ...
0
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0answers
23 views

Fitting a Non-Central t-Distribution with Location and Scale Transformations

I am trying to fit a distribution function to empirical observations that have the following properties: Non-zero mean Non-unit variance Heavy tails Asymmetric about the mode I am considering ...
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0answers
34 views

Linear-logarithmic Regression in MATLAB with two input arguments - which model to assume?

Look at the following plot and ignore the solid lines please (just look at the dotted/dashed ones). ONE curve is described by the following parameters and ONE fixed value for the second input ...
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1answer
61 views

Fitting distribution to spatial data

Cross posting my question from mathoverflow to find some stats specific help. I am studying a physical process generating data which projects nicely into two dimensions with non-negative values. ...
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0answers
31 views

Fitting Inspection Time Data to Curve

I have a set of Inspection Time data that consists of two variables: SOA (stimulus onset asynchrony) and Accuracy. This data refers to how accurately you can perform on a simple stimuli ...
3
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1answer
132 views

Find out if there is a way to create BMI weight category variable

I am working on a project and have to find a way to break my data into percentiles. The variables that I already have are gender, age in months and BMI. If I am able to calculate the percentile that ...
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0answers
42 views

Fitting a model to correlated data

Trying to fit a model (bloch equations from MRI) to experimental data (12 parameters, 12 equation). Monte Carlo Multistart ('lsqcurvefit' in MATLAB) gives expected values for all parameters except for ...
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0answers
24 views

Fitting a function to data with correlated errors

I have a question regarding fitting a curve to data with correlated uncertainties. Suppose I have 8 bins each with uncertainties (img below). The green line is theory curve I am trying to fit with a ...
0
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0answers
98 views

How do I regularize Python scipy's curve_fit when performing linear regression?

I have recently become proficient at using Python/scipy curve_fit to perform linear regression. However, with higher order ...
0
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0answers
32 views

Generating artificial experimental data to test model fitting software

I wish to test some model fitting software and I would like to generate synthetic datasets for this test. The synthetic data is supposed to originate from a experiment that measures the change in ...
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0answers
38 views

Optimal Rotation Before Curve Fitting

I am fitting a 1-dimensional polynomial to a set of data points $\{(x_1,y_1,z_1),...,(x_N,y_N,z_N)\} \subset \mathbb{R}^3$ using least squares regression. My first instinct was to choose $x$ as an ...
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0answers
66 views

Bayesian inference and curve fitting

I'm a silly scientist, and I've got a process I'm interested in. It gives me lots of time-series data. I've got an explicit, analytical model that is firmly rooted in reality, and basically boils down ...
0
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1answer
29 views

Cross fitting with same params but differents models

What is the best fitting way with 2 variables to explain ($Z_1$ and $Z_2$) depending on the same variables ($X$ and $Y$) and parameters $\theta$ but with differents models ($f$ and $g$)? For ...
2
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1answer
94 views

Fitting two sets of values by changing x-axis

I have two datasets. The first one consist of measurements with a known date. The second dataset consists of measurements along a distance axis. The second dataset is sequentially deposited (for ...
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3answers
178 views

Fitting data to describe data the best way

This data is for a company who wants to minimize their expenses. The expenses is described out of the production costs . (Production, salary, capital and material prices). I need to create a ...
1
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3answers
158 views

R - Find curve pattern of simple time series

I have time series data of credit card transaction volumes for different companies. For example: week1: \$5000 week2: \$6000 week3: \$6200 week4: \$7000 week5: \$9000 ... Is there a simple method in ...
1
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1answer
42 views

What is the standard format of the equation that represents the production of this daughter isotope?

I have an idea about producing a genetic algorithm. But it involves using a relationship which believe could be defined as a horizontal Asymptote. I have found an image that depicts the type of ...
0
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1answer
76 views

Fitting NLS algorithm

I have the list of time series. I am fitting these series with the formula $$y=ax^2\exp(b*x)$$. It should be noted that parameter $b$ in the formula must be negative as this reflects the behaviour of ...
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0answers
55 views

Finding underlying distribution of proportion data

I have a large dataset of count data --- count of positive cases and total number of cases distributed by distance (in meters). The empirical distribution of proportions and beginning of data are ...
2
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0answers
82 views

Comparing facial curvature of two human faces

I need help determining if what I'm doing is sufficient. I have extracted the "curvature" from two human faces (essentially the curve that goes from one ear, down the face to the chin, and back up to ...
1
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1answer
55 views

How to algorithmically determine the best order of fit?

I am doing a least squares polynomial interpolation for 10,000 data sets that look mostly like one period of a sine curve, but whose values are not evenly spaced in the time domain, and can sometimes ...
0
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0answers
29 views

Least squares minimization with unweighted data

A couple of questions regarding least squares minimization with unweighted data: 1) Assuming you do not have any estimates of errors/weights for data, is there any way to provide a goodness of fit? ...
0
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0answers
55 views

Bimodal curve fitting

I have been at it for days and simply can't solve this. I would like to fit a curve with two peaks (i.e. bimodal) to my data set. I have both x and y values in my data (i.e. not a probability ...
8
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1answer
200 views

Estimating the slope of the straight portion of a sigmoid curve

I have been given this task and was stumped. A colleague asked me to estimate the $x_{upper}$ and $x_{lower}$ of the following chart: The curve is actually a cumulative distribution, and x is some ...
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0answers
40 views

Obtaining an estimate of slope error on a linear fit to data with y error

I have a problem similar to what was discussed here: I have a dataset (x_i,y_i) with y-error which is nonuniform over the interval of interest. I want to fit a line to this and extract a value of ...
4
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1answer
139 views

Chi-Squared Formula

I have several nonlinear curves of the transmission spectrum of a semiconductor. I got a fit to each of the curve. To get the chi squared for each my teacher gave me the formula ...
0
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2answers
160 views

Distribution fitting on empirical PDF?

I have a class of distributions that I think may have generated some data I have, and would like to find the best fit distribution and corresponding parameters. But the data I have aren't samples from ...
4
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3answers
248 views

Linear regression best polynomial (or better approach to use)?

Any ideas on other polynomials I could successfully use for applying regression? My goal is a solution that has fit error strictly based on the noise. Is this possible since it is a bell-like curve? ...
1
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1answer
99 views

How to use the Pareto distribution in fitting survival curves?

I have a series of numbers, which are some survival probabilities that form a decaying curve. I would like to fit them with a "Pareto" distribution. I expect to have a smooth fitted curve, thus I can ...
2
votes
1answer
41 views

How do I incorporate 2 peaks in a liquidity model using curve-fitting and nls

This is my first time at stack exchange, hence please pardon me if I miss something. I have multiple questions and I am tearing myself as curve-fitting and estimation is foreign land to me, I am ready ...
0
votes
1answer
233 views

Fitting discrete points on a normal distribution

I have an ordinal ranking of 16 objects. I know that the value of the first object is 0, the second value is 2, and the last object is 14. I'd like to map each of the intermediate objects to an ...
1
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1answer
966 views

Maximum Likelihood Curve/Model Fitting in Python

I have some 2d data that I believe is best fit by a sigmoid function. I can do the fitting with the following python code snippet. ...
0
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0answers
79 views

Estimate shifted log Gamma parameters via L-Moments

L-Moments and Probability Weighted Moments are a very robust estimation method for some cases; in particular for the Generalized Extreme Value distribution they seem to be the method of choice if it ...
0
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2answers
57 views

Clustering cloud fitting inverse functions

I have a cloud of points that can be clustered so that each set of points in the cluster can be fitted with an inverse function : $f(x) = cte / x$. What would be an approach for clustering my dataset ...
0
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0answers
128 views

Statistics for comparing curve fitting models

I would like to get some statistical advice. I have individuals from which longitudinal growth data are collected (their growth curves with yearly measurements). This growth data I’ve fitted by ...
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0answers
103 views

How can I change my fitting method to force better relative accuracy instead of just absolute accuracy?

I have some data which I want to use for interpolation and extrapolation. I would (very much) prefer a function that I can plug values in instead of using cubic splines or some such technique so I ...
0
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0answers
94 views

Finding exponent of power-law relation between two variables

My question is related to two previous questions here: Strange outcome when performing nonlinear least squares fit to a power law Exponent for non-linear regression (in R)? unfortunately, I lack ...