Hi,
I think you can pass whatever you want for those parameters since they are actually not used in the algorithm.
The only thing that is used it the topology.
Actually the fruchterman algorithm in 1.40 was broken and did not work for me.
Maybe you should give the newly released 1.41 a try because there the two parameters origin and extend have been removed and the bug that was in 1.40 has been fixed.
Best
Ralph