Create a connectivity matrix where each incoming edge becomes outgoing.

def reversed(self):
        """Create a connectivity matrix where each incoming edge becomes outgoing."""
        n_rows = len(self)
        reversed = DirectedAdjacencyMatrix(n_rows, self.dtype)
        for r, row in enumerate(py.prog_iter(self)):
            for c in row:
                reversed[c].append(r)
                
        return reversed