def print_flow(self):
        '''
        API:
            print_flow(self)
        Description:
            Prints all positive flows to stdout. This method can be used for
            debugging purposes.
        '''
        print('printing current edge, flow, capacity')
        for e in self.edge_attr:
            if self.edge_attr[e]['flow']!=0:
                print(e, str(self.edge_attr[e]['flow']).ljust(4), end=' ')
                print(str(self.edge_attr[e]['capacity']).ljust(4))
API:
            print_flow(self)
        Description:
            Prints all positive flows to stdout. This method can be used for
            debugging purposes.