survival {samc}

Calculate survival metrics

Description

Calculates the expected time to absorption

Usage

survival(samc, init, origin)

## S4 method for signature 'samc,missing,missing'
survival(samc)

## S4 method for signature 'samc,missing,location'
survival(samc, origin)

## S4 method for signature 'samc,ANY,missing'
survival(samc, init)

Arguments

samc

A samc-class object created using the samc function.

init

Sets the initial state \psi of the transients states. Input must be able to pass the check function when compared against the samc-class object. Can only contain positive finite values.

origin

A positive integer or character name representing transient state \mathit{i}. Corresponds to row \mathit{i} of matrix \mathbf{P} in the samc-class object. When paired with the dest parameter, multiple values may be provided as a vector.

Details

z=(I-Q)^{-1}{\cdot}1=F{\cdot}1

• survival(samc)

  The result is a vector \mathbf{v} where \mathbf{v}_i is the expected time to absorption if starting at transient state \mathit{i}.

  If the samc-class object was created using matrix or RasterLayer maps, then vector \mathbf{v} can be mapped to a RasterLayer using the map function.

\psi^Tz

• survival(samc, init)

  The result is a numeric that is the expected time to absorption given an initial state \psi.

Value

See Details

Performance

Any relevant performance information about this function can be found in the performance vignette: vignette("performance", package = "samc")

Examples

# "Load" the data. In this case we are using data built into the package.
# In practice, users will likely load raster data using the raster() function
# from the raster package.
res_data <- samc::example_split_corridor$res
abs_data <- samc::example_split_corridor$abs
init_data <- samc::example_split_corridor$init


# Make sure our data meets the basic input requirements of the package using
# the check() function.
check(res_data, abs_data)
check(res_data, init_data)

# Setup the details for a random-walk model
rw_model <- list(fun = function(x) 1/mean(x), # Function for calculating transition probabilities
                 dir = 8, # Directions of the transitions. Either 4 or 8.
                 sym = TRUE) # Is the function symmetric?


# Create a `samc-class` object with the resistance and absorption data using
# the samc() function. We use the recipricol of the arithmetic mean for
# calculating the transition matrix. Note, the input data here are matrices,
# not RasterLayers.
samc_obj <- samc(res_data, abs_data, model = rw_model)


# Convert the initial state data to probabilities
init_prob_data <- init_data / sum(init_data, na.rm = TRUE)


# Calculate short- and long-term metrics using the analytical functions
short_mort <- mortality(samc_obj, init_prob_data, time = 50)
short_dist <- distribution(samc_obj, origin = 3, time = 50)
long_disp <- dispersal(samc_obj, init_prob_data)
visit <- visitation(samc_obj, dest = 4)
surv <- survival(samc_obj)


# Use the map() function to turn vector results into RasterLayer objects.
short_mort_map <- map(samc_obj, short_mort)
short_dist_map <- map(samc_obj, short_dist)
long_disp_map <- map(samc_obj, long_disp)
visit_map <- map(samc_obj, visit)
surv_map <- map(samc_obj, surv)