fit_gompertz: Fit Gompertz model

In rumenGP: Rumen Gas Production Modeling, Comparison, and Visualization

Fit Gompertz model

Description

Fits the Zwietering-modified Gompertz model to each bottle in a rumen_gp dataset.

Usage

fit_gompertz(data, start = NULL)

Arguments

data	A rumen_gp object.
start	Optional list of starting values. May contain any of: A mu lambda

Details

Equation

V(t)= A \exp \left[ - \exp \left( \frac{\mu e}{A} (\lambda-t) + 1 \right) \right]

where:

• V(t) is cumulative gas production at time t

• A is asymptotic gas production

• \mu is the maximum gas production rate

• \lambda is lag time

• e is Euler's number

Interpretation

The modified Gompertz model is one of the most commonly used models for gas production kinetics.

It explicitly estimates:

• Final gas production potential (A)

• Maximum gas production rate (\mu)

• Lag time (\lambda)

making it biologically informative and easy to interpret.

Advantages

• Explicit lag parameter

• Explicit maximum gas production rate

• Excellent flexibility

• Widely used in gas production studies

• Strong biological interpretation

Limitations

• More computationally demanding than simple exponential models

• Parameters may exhibit correlation in some datasets

Value

A gompertz_fit object containing:

• Parameter estimates

• Model diagnostics

• Predicted values

• Residuals

Examples

files <- example_data()

raw_data <- read_ankom(
  files$ankom
)

metadata <- read_metadata(
  files$metadata
)

gp <- process_ankom(
  raw_data,
  metadata,
  headspace_ml = 210,
  temperature_c = 39
)

# Fit using package default starting values
fit_default <- fit_gompertz(
  gp
)

summary(fit_default)

# Fit using custom starting values
fit_custom_start <- fit_gompertz(
  gp,
  start = list(
    A = 120,
    mu = 5,
    lambda = 1
  )
)

summary(fit_custom_start)

rumenGP documentation built on Oct. 2, 2026, 5:09 p.m.