Questions tagged [nls]
`nls` is an R routine to fit nonlinear regression models of the form $y = f(x B) + e$
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How can I transfer the exponential relationship to linear?
The exponential relationship between y and x I got is
model_1 <- nls(y ~ I(a * exp(-b * x)),
start = list(a = 1, b = 0), trace = TRUE)
...
1
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1answer
29 views
How to calculate time of day of the peak of a harmonic function fit from phase offset estimate from R nls
I'm trying to calculate the time of day of a harmonic function peak using nls() in R. I've looked at the posts here, here and here, but have not found a method to calculate time of day from phase ...
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12 views
NLS more consistent than GMM
I'm trying a simple code to test whether NLS has better performance than GMM. The R code looks like this
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0answers
21 views
Why SSgompertz does not work on similar data sets?
I have data that follows a sigmodial shape and the Gompertz function seem to make sense. I wanted to use SSgompertz in nls to find the parameters, but I get sometimes errors. So, I wanted to learn ...
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54 views
Start function issues using nls
I want to statistically compare two curve fitting from two different dataset : pA3 et pE5. They both follow sigmoid curves (I do not use high enough concentration of pA3 to see the lower plateau). So ...
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1answer
23 views
Fitting a non-linear least squares regression to estimate coefficients of parameters in R
I need to fit a non-linear least squares regression to estimate coefficients which are governed by an equation that have parameters obtained from generating data series.
Data:
...
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0answers
20 views
Test for equal variance of residuals for Nonlinear Regression Models?
I obtain a residual plot against the fitted values and it does show some pattern for the residuals, so I suspect there may exists heteroskedasticity problem. Which kinds of test can be apply here to ...
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21 views
Get initial parameters for growth models with nls whith non-common functions like “Ricker2” or “Richards” functions
I usually fit the most commonly known growth models using the FSA library and with the function selfStart.
Now, I am trying to test some models with the Original Gompretz vbFuns("Ricker2") ...
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1answer
33 views
Is a Google Sheets fit model a valid place to retrieve starting parameters for nls() in R Studio?
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I am trying to fit an exponential model of form y = ae^(xb) in R to the data I have ran below, using the nls() function. I have read here and in other places that I need to feed the model reasonable ...
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28 views
Basic assumptions: Difference between the normality test in data and in the analysis of variance model
I have two situations that finish in a conceptual question. Linear models (lm) and non-linear models (nls) need to be normality assumptions, but what is the difference between the normality test in ...
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1answer
78 views
How to fit a piecewise assembly of nonlinear functions?
I am trying to model vegetation spectral signatures (grey lines) using a two-part piecewise function (black dotted lines). In it, I am trying to use only a few points (red dots) to fit a linear (first ...
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21 views
How to choose suitable nls models?
I'm trying to run nls models in two datasets using the sigmoid model, but the models are poor.
How can I chose suitable models?
The datasets are from n. animals harvested per species by 30 villages, ...
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68 views
using nls in R to fit a distribution to a model - constant error on multiple parameter estimate
I have a distribution of data (x), which I need to fit with a two-species, or three-species model (essentially the sum of two gamma distributions) to find D (the diffusion coefficient).
A single-...
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1answer
99 views
NLS analysis in R with timeseries data to remove known effect
I have a timeseries dataset collected by sensors. The data is crack displacement (disp) and temperature (temp). Thermal ...
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0answers
14 views
estimating non linear function depending on 2 factors - possibly using gams
I have data like this and I already used a gam for geom smooth:
Every scatter is for each month (first factor) and x is an integer. There is another 2 level factor. For one level the response is more ...
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1answer
28 views
fitting specific formula/model in r - model possibly not identifiable
I would like to fit the following formula in R:
y ~ alpha *(x1_0 * x2_0 * beta_0 + x1_1 * x2_1 * beta_1)
Here: alpha, ...
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0answers
18 views
fitting multiplicative non linear model in R
I have samples per month over several years (assuming stationary behavior). My data contains an independent variable: hours (representing available hours per month). The model to be fitted should ...
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14 views
Nonlinear regression with variables that are directly dependent on each other
I am performing a nonlinear regression analysis (with the nls function in r) to estimate the constant parameters for a proposed equation. My equation has 4 variables L, G, m, and S. G and S are not ...
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2answers
293 views
Interpreting and troubleshooting nls in R with quadratic plateau model
I am trying to run a quadratic plateau model on some proportion data where values are bound between 0 and 100. I would like some help troubleshooting some errors I have encountered, and correctly ...
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3answers
257 views
How do you compare linear model vs non-linear (nls) model in R?
I am trying to model some data, and as part of the modeling, I tried linear model (using lm function) and non-linear model (using nls) function.
Model 1 : a linear model which has degrees of freedom ...
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0answers
364 views
Starting values for an nls model in R [duplicate]
I'm trying to fit an exponential model using nls, but I don't know how to select the starting values for the parameters. I know this question has been answered multiple times, but I spent some days ...
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1answer
82 views
Sine curve fit and model tunning using nls in R
I acquired data (motor adaptation =y in function of delays =t ) which I expect to look like a sine wave. I am trying (1) to fit a sine curve in my data and (2)to estimate the best model/parameters. I ...
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381 views
Sine curve fit using nls in R
I acquired data (motor adaptation $y$ as a function of delays $t$ ) which I expect to look like a sine wave. I am trying (1) to fit a sine curve in my data and (2) to estimate the best model/...
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0answers
18 views
Sine curve fit using lm, nls and nls2 in R [closed]
I acquired data (motor adaptation =y in function of delays =t ) which I expect to look like a sine wave. I am trying (1) to fit a sine curve in my data and (2)to estimate the best model/parameters.
I ...
0
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1answer
227 views
Comparing time series data between three treatment groups (in R)
I have time series data where the response is decreasing over time. The rate of the decrease is supposed to depend on the treatment (the concentration of a drug). By looking at the data I am not sure ...
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42 views
r - Understand goodness of a fitted curve [duplicate]
I had to find the equation of curve that represent my data. After trying different function, I got a models that seems fitting my data, at least by plotting them. But this is it. I have no idea how to ...
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1answer
813 views
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211 views
Constraining parameters in NLS in R to be less than a value, or greater than a different value
The nls function in R comes with upper and lower arguments to specify the upper or lower ...
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0answers
34 views
Nonlinear fit in R only works with tightly restricting parameter bounds [duplicate]
I have a reproducible example here with an attempt to use nls to fit a nonlinear function:
y = ax/(b+x) + c
Even when I set the starting values to be a good, ...
0
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1answer
992 views
Singular gradient erros, NLS in R
I'm trying to fit nls(Mound~ a*kg.bag.collar^b + c, start = list(a = 83, b = -.5, c=100), data=test) using the dataset here. I've fit it without trouble without the ...
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0answers
672 views
NLS model comparisons by ANOVA
I am comparing NLS models from two groups, males and females. I compared the models by ANOVAs, but I am hesitating which is the correct model comparison to use:
a) Subgroup Males vs Subgroup Females
...
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0answers
147 views
Trouble fitting my data with non-linear Regression model
I have a dataset that contains tree height and diameter measurements among the tree stem. I tried to fit my data with GNLS in R, but I'm getting this "step halving factor reduced below minimum in NLS ...
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0answers
19 views
Estimate the Beta Coefficients, and then find an algorithm
Referring to the photo, I need to report my beta coefficients as functions of observed Xi and Yi. I tried to reduce by taking the log of both sides but It seems I can't reduce this model because it is ...
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595 views
Initial conditions for nonlinear models using the nlsLM function
I have a data frame containing 70000 rows. For each row, I am trying to apply the nlsLM function (minpack.lm package) to find ...
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0answers
148 views
comparison of more than one multivariate nls models in r
dear members,
I am trying to identify which of the two multivariate nls models is more of a good fit. I came to know that you can use anova and f tests for univariate nls models to know ...
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1answer
1k 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
82 views
Reproducing non-linear sigmaplot regression with nls()
I'm trying to reproduce a non-linear regression with various similar datasets.
The original regressions were performed by sigmaplot with a modified morrison equation and estimates for parameters E=2,K=...
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0answers
3k 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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0answers
256 views
Why do different parameterizations give different results for nls?
Goal
I'm trying to fit a four-parameter logistic (A+(B-A)/(1+exp((xmid-input)/scal))) in R, using nls and SSfpl, to fit two datasets that share the upper, lower, ...
3
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1answer
2k views
Standard errors for non-linear least squares in R
I have a question on standard errors for non-linear least squares in R. With the built-in function NLS and a hand-made function I get different SE and I don't understand why. I will try to expose ...
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0answers
570 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
3k 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:
...
1
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1answer
317 views
Difference between probit of log(x) and probit using inverse lognormal cdf of x
Topic: probit and logprobit regression.
Context: I have to implement a model of size at maturity in a wild population and I must choose a binomial linear model to estimate the parameters based on ...
2
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0answers
319 views
Bootstrapping of nonlinear regression residuals: why does the model fitting fail?
I am trying to define a range of uncertainty associated with each estimate of the parameters of a nonlinear model:
...
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2answers
9k views
Fitting exponential decay with negative y values
I am trying to fit an exponential decay function to y-values that become negative at high x-values, but am unable to configure my nls function correctly.
Aim
I ...
0
votes
1answer
360 views
Fitting a non linear equation to a dataset
I am working on fitting an equation from a dataset. In my dataset I have two variables where I am interested at and I looking a function that gives me the value the free variables that I use in the ...
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2answers
706 views
How to calculate p-value for a parameter given confidence interval when null hypothesis != 0
Given the dataset:
...
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1answer
1k views
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1answer
2k views
nls() gradient error in fitting growth curve data
I am trying to model the following data on promotional budget and customer awareness. The idea is, at some point, increase in budget doesn't have any further impact on awareness; it saturates.
...
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2answers
2k views
nls() function in R not fitting well when calculating Kd
I'm trying to calculate Kd with the following R code but my model is clearly wrong (see image). How has nls() converged so poorly? How can I use it to find a better ...
