Description Usage Arguments Value Author(s)

If more than one area is defined the user can define migration
between the areas. The migration procedure is the same as in MULTSPEC.
The migration is defined and takes place in every timestep and it is
assumed to be constant for all years. This means that the porportion that
migrates from area i to j can be different between different timesteps
(seasons) but they are fixed between observations (years). Migration at
timestep t is defined by the user as an *nxn* transition
matrix P_t := [p_ij] where p_ij is the proportion moving from area j
to area i, ignoring other processes. For P to be a transition matrix
*sum_i p_ij = 1*, for each j. The vector of abundance
for all areas at time t is therefore:

*N_t = P_t N_{t-1}*

In a two area example this would mean that if N_1,t-1 is a matrix containing the abundance in numbers in area 1 at timestep t before migration and N_2,t-1 is the same number for area 2, the numbers after migration will be

*N_{1,t} = p_{11}\cdot N_{1,t-1} + p_{12}\cdot N_{2,t-1} *

*N_{2,t} = p_{21}\cdot N_{2,t-1}+ p_{22}\cdot N_{2,t-1} *

1 | ```
migrate(N, M)
``` |

`N` |
An array containing substock abundance by area (first dimension) and other variables |

`M` |
an array with migration matricies |

the migrated substock abundance array

Bjarki Þór Elvarsson

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