test of force as derivative of the potential for SnapshotPotential, related to #215
test of force as derivative of the potential for SnapshotPotential, related to #215

jobovy/galpy,followthesheep/galpy,jobovy/galpy,followthesheep/galpy,followthesheep/galpy,followthesheep/galpy,jobovy/galpy,jobovy/galpy