Improve price_network() seeding semantics
Now, if 'm' is larger than the seed graph, it is set to the size of the seed graph, and is increased progressively until it matches the desired value. This removes the need to start with a random seed graph of the appropriate size. This also includes modifications which make the code more robust against parameter choices which don't make much sense, e.g. lead to negative probabilites.
Showing with 35 additions and 18 deletions