```
def trips_ij(Ti, mi, mj, sij):
"""
Radiation model (see the paper "Universal predictability of mobility patterns in cities")
Predict travel fluxes among the locations i and j based on population distribution
Parameters
----------
Ti: int
Total trips departing from i
mi: int
Population at location i
mj: int
Population at location j
sij: int
Total population in the circle with center i and radius rij
(excluding i and j)
Returns
-------
Tij: int or float
number of trips departing from location i to location j
"""
Tij = Ti * (mi * mj) / ((mi + sij) * (mi + mj + sij))
return Tij
```