7.4 Some additional remarks

Note that user provided functions should return a backward migration matrix. You can, however, in cases where this is more natural, specify a model for the forward matrix, and then, before returning the resulting matrix, convert it to a backward matrix, with the forw2back function. This function takes a forward matrix as its first argument and a vector of subpopulation sizes as its second argument and returns a backward matrix (Tufto et al., 1998, eq. 5).

User provided functions specifying a model for the migration matrix may, of course, incorporate dependencies on additional information, say the geographic location (e.g. Tufto et al., 1998) or habitat quality of different subpopulations, through the use of global variables.