<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def num_coll_reqd(DIM_FRACTAL, material, DiamTarget):
 """Return the number of doubling collisions required. Calculates the number of doubling collisions required to produce a floc of diameter DiamTarget. """

    return DIM_FRACTAL * np.log2(DiamTarget/material.Diameter)