Questions tagged [nls]
`nls` is an R routine to fit nonlinear regression models of the form $y = f(x B) + e$
113
questions
0
votes
0
answers
18
views
Advice on fitting curve to three-pooled plant decomposition model in r
I have just finished running a plant decomposition experiment measuring the decomposition of pine needles across climate and lithological types. We have mass loss, plant chemistry data (c, n, labile ...
0
votes
1
answer
58
views
Fitting a cubic-like curve to data in R
I tried using nls() in R to fit the following expression to a set of data:
where g=9.8, alpha & B_0 are unknown, a = 0.01, z_0 = 0.3 such that:
theory <- as.formula(V~-(9.8)ab*(pi)(0.02^2)(T)(...
- 3
2
votes
0
answers
27
views
Seeking a combination of nls() params that would make this fit curve slightly more acute?
I have some data with fields GrowthRate and DAY. GrowthRate. E.g. If amount is 100 on day 1 and then 110 on day2, GrowthRate is 1.1. Data look like this:
...
- 1,228
0
votes
1
answer
72
views
Modelling poisson distribution with nls() in R?
I'm trying to model the probability that somebody can do a 90 day Snapchat streak. I have some binary success data in the form of count data (the participant only reached 90 days once):
I've ...
- 3
0
votes
0
answers
9
views
Best approach to compare trends in timepoint measurements
I have two datasets, a control and experiment.
Composed of "activation measurements" of cells(y) on fixed time points with uneven intervals (x). At each time point cells from one batch are ...
- 11
0
votes
0
answers
31
views
Test effects of multiple categorical variables in a nonlinear model
I am fitting forest biomass data to a modified version of the Chapman-Richards function using the nlsLM() function.
I am curious about the impact of multiple binary predictor variables on the model. ...
0
votes
0
answers
27
views
nonlinear least square optimization for Logistic Regression
Generally I have trained a logistic regression model with:
...
- 113
2
votes
1
answer
46
views
Correct GLM or NLS to model exponential model with response variable with positive and negative values
I have been struggling to find the right way to model this dataset, this is a Data Frame with the dataset:
...
- 343
0
votes
0
answers
37
views
R - problem with fitting to a custom non-linear equation
I have a problem. In GraphPad Prism, fitting to the following equation
my data produce pretty nice results. However, when I try to repeat in R, it generates terrible output. Here is the code:
...
0
votes
0
answers
35
views
Using the FSA R package to test effect of continuous covariates on von Bertalanffy growth rate
Is it possible to use the FSA package in R to test for the effect of continuous variables (such as temperature, latitude, precipitation). I have recapture growth data and am able to test for the ...
0
votes
1
answer
84
views
Fit exponential decay upwards model - start values give 'convergence failure'
I have some data that when plotted looks similar to this:
Then eyeballing the charts on this page, it looks like I might have an exponential decay (Increasing form) relationship?
I searched for how ...
- 1,228
0
votes
1
answer
43
views
Parametric nonlinear term in mgcv
The R library mgcv can handle both parametric linear and non-parametric non-linear terms, but is there any way to let it handle parametric non-linear terms?
For ...
- 163
0
votes
0
answers
7
views
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 <-...
0
votes
0
answers
12
views
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:
...
- 1
0
votes
1
answer
110
views
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 ...
- 187
1
vote
0
answers
59
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 (...
- 11
1
vote
0
answers
227
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 ...
- 11
0
votes
1
answer
46
views
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
1
vote
1
answer
71
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 ...
- 11
0
votes
0
answers
59
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 ...
0
votes
1
answer
78
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:
...
- 113
0
votes
1
answer
107
views
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 ...
- 1
3
votes
1
answer
244
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 ...
- 51
1
vote
0
answers
210
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-...
- 11
1
vote
1
answer
198
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 ...
- 61
0
votes
1
answer
32
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, ...
- 1,306
6
votes
2
answers
544
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 ...
- 113
1
vote
3
answers
666
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 ...
- 11
0
votes
0
answers
733
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 ...
- 1
1
vote
1
answer
147
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 ...
- 11
0
votes
0
answers
953
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/...
- 11
0
votes
0
answers
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 ...
- 11
0
votes
1
answer
607
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 ...
- 3
1
vote
0
answers
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 ...
- 31
0
votes
1
answer
1k
views
2
votes
1
answer
432
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 ...
- 463
0
votes
0
answers
65
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, ...
- 463
0
votes
1
answer
2k
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 ...
- 280
1
vote
0
answers
972
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
...
- 106
0
votes
0
answers
216
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 ...
1
vote
0
answers
20
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 ...
- 11
0
votes
0
answers
858
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 ...
- 103
2
votes
2
answers
249
views
The non-linear extra sum of squares? What is this?
I encountered in the article I read the term the non-linear extra sum of square with the reference to Bates and Watts 1988. I do ...
- 111
0
votes
0
answers
183
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 ...
4
votes
1
answer
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.
...
- 143
0
votes
0
answers
111
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=...
- 135
3
votes
0
answers
4k
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 ...
2
votes
0
answers
277
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
votes
1
answer
3k
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 ...
- 43
4
votes
0
answers
705
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 ...
- 481