vertex_updater: Edge propagation instance Executes a callback on the edge...
In robertness/lucy: Really useful things done with graphs.

Edge propagation instance Executes a callback on the edge that calculates a value. The callback can rely on values of other edges that are calculated by the same callback. When the function is applied to an edge, it checks that an 'update' attribute on all the edges that it relies on is set to true before applying the callback. If not, the callback is applied to those unupdated edges first.

1	vertex_updater(g, v, get_determiners, callback, verbose = FALSE)

`g`	an igraph object
`get_determiners`	a function that returns the indices of the edges that must be updated before the callback is executed.
`verbose`	if TRUE prints out details of propagation
`e`	an index for an edge in g
`a`	function that performs an operation on an edge.