fit_brody: Fit Brody model

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

Fit Brody model

Description

Fits the Brody gas production model to each bottle in a rumen_gp dataset.

Usage

fit_brody(data, start = NULL)

Arguments

data	A rumen_gp object.
start	Optional list of starting values. May contain any of: A b k

Details

Equation

V(t) = A \left(1 - b e^{-kt}\right)

where:

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

• A is asymptotic gas production

• b is an integration constant

• k is the fractional rate constant

Interpretation

The Brody model describes gas production as a monotonic increase toward an asymptotic value. The parameter k controls the speed of fermentation, while b controls the initial position of the curve.

Advantages

• Simple and robust

• Stable convergence

• Easy biological interpretation

• Useful as a baseline model

Limitations

• No explicit lag parameter

• Less flexible than sigmoidal models

• May not adequately represent strongly sigmoidal fermentation profiles

Value

A brody_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_brody(
  gp
)

summary(fit_default)

# Fit using custom starting values
fit_custom_start <- fit_brody(
  gp,
  start = list(
    A = 120,
    b = 0.9,
    k = 0.05
  )
)

summary(fit_custom_start)

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