fit_expl: Fit exponential model with lag (EXPL)

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

Fit exponential model with lag (EXPL)

Description

Fits the exponential gas production model with an explicit lag phase.

Usage

fit_expl(data, start = NULL)

Arguments

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

Details

Equation

V(t) = Vf \left(1 - e^{-k(t-\lambda)}\right)

where:

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

• Vf is asymptotic gas production

• k is the fractional rate constant

• \lambda is lag time

Interpretation

The EXPL model assumes that gas production follows an exponential pattern after a lag phase. The lag parameter represents the delay before substantial fermentation begins.

Advantages

• Explicit lag parameter

• Simple biological interpretation

• Stable convergence

Limitations

• Less flexible than sigmoidal models

• May not adequately represent multiple fermentation phases

Value

An expl_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_expl(
  gp
)

summary(fit_default)

# Fit using custom starting values
fit_custom_start <- fit_expl(
  gp,
  start = list(
    Vf = 120,
    k = 0.05,
    lambda = 1
  )
)

summary(fit_custom_start)

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