sigmap: Access or assign the process error

In cttedwards/bdm: Bayesian biomass dynamics model

Access or assign the process error

Description

By default the bdm package assumes that the process error variance is fixed on input and specified in the bdmData object class. This function can be used to access or assign the standard deviation \sigma_p within an bdmData object.

Usage

sigmap(object, ...)

## S4 method for signature 'bdmData'
sigmap(object)

sigmap(object) <- value

## S4 replacement method for signature 'bdmData,numeric'
sigmap(object) <- value

Arguments

object	an bdmData object
...	additional arguments to the generic function
value	a numeric value for \sigma_p

Details

Process error is used to refer to the deviation of the process equation from the deterministic expectation:

E[B_{t+1}] = max(B_{t} + g(B_{t}) - H_{t}, 0)

where B is the biomass, g() is the production function and H is the catch (or harvest). The process error is assumed by default to follow a log-normal distribution:

B_{t+1} \sim LN(ln(E[B_{t+1}])-\sigma^2_p/2, \sigma^2_p)

Realistic values for the process error are typically 0.05 < \sigma_p < 0.15. The default value is \sigma_p = 0.05.

Value

Accessor function returns a numeric value. Assignment function populates the bdmData object.

Examples

# initialize bdmData object
dat <- bdmData(harvest = 20:30, index = runif(11))

# assign and access sigmap
sigmap(dat) <- 0.1
sigmap(dat)

cttedwards/bdm documentation built on June 11, 2025, 5:17 p.m.