# 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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### Why does NSL report Std. Err that is equivalent to the NIST reported SD

I am running a verification using the NISTnls package (https://cran.r-project.org/web/packages/NISTnls/NISTnls.pdf). When I used the example code for the supplied functions, e.g. Chwirut1: result <-...
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### How do I calculate my a and b start parameters in NLS [duplicate]

I'm trying to fit an exponential decay curve to my data to measure copies of DNA left over time, with no luck. Here is my dataframe: ...
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### How to run a nls for multiple dependent variables?

I am unfamiliar with nls however after doing some research on the function it seems to be appropriate for my current analysis. I am testing population declines over ...
29 views

### Sum of two gaussian curves

I have a set of raw chromatographic data (x,y) where I'm trying to evaluate the area of two unresolved peaks separately using gaussian approximations in R. I found this answer from a few years ago (...
21 views

### Calculate residence time from double exponential fit

I did a tracer addition experiment. I added a tracer in Mass 1 (see figure), the tracer moves from Mass1 to Mass2 and then to Mass3 and so on. The flow of the tracer between the mass happens over days....
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### R: Estimation using nls() in Poisson - INAR(1)

This is a Poisson-INAR(1) that I want to use for my data. My purpose is to find estimation of rho_{i,t} and lambda_{i,t} using nls(). But I cannot figure how it can works for my model. Any suggestion ...
121 views

### Quantile regression with an exponential function

The following equation: y = a*x**b where y is a nonlinear function of x. By taking logs, the equation can be expressed as: ln(y) = ln(a) + bln(x). I would like to run a quantile regression instead of ...
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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) ...
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### 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 ...
16 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 ...
28 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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### 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 ...
32 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: ...
34 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 ...
37 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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### Is a Google Sheets fit model a valid place to retrieve starting parameters for nls() in R Studio?

0 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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### 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 ...
115 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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### 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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### 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, ...
380 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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### 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 ...
527 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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### 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 ...
613 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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### 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 ...
376 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 ...
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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### 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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### 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, ...
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### 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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### 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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### 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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### 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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### 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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### 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 ...
2k 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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### 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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### 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 ...
263 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, ...
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### 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 ...
624 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 ...
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### 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: ...
344 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 ...
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### 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: ...
10k 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 ...
380 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 ...