We need to assign radio frequencies to a set of transmitters in a telecommunication network. 
Each transmitter must be assigned a frequency from a given set of available frequencies. 
The objective is to minimize interference between transmitters while using the minimum number of distinct frequencies.
The interference between two transmitters is proportional to the square of their geographical distance and the absolute difference between their assigned frequencies.
Each transmitter must be assigned exactly one frequency.
The frequency assigned to a transmitter must be within its allowed frequency range.
Transmitters that are geographically close to each other must have a minimum frequency separation to avoid interference.
Some transmitters may have pre-assigned frequencies that cannot be changed. Pre_assigned_frequency of -1 means no pre-assignment.

Example input data:
1. transmitters.csv
transmitter_id,x_coordinate,y_coordinate,min_frequency,max_frequency,pre_assigned_frequency
T1,10,20,1,10,-1
T2,15,25,1,10,-1
T3,30,40,1,15,-1
T4,35,45,1,15,7
T5,50,60,5,20,-1

available_frequencies.csv
frequency_id,frequency_value
F1,1
F2,2
F3,3
F4,4
F5,5

3. interference_matrix.csv
transmitter1_id,transmitter2_id,min_frequency_separation,interference_cost
T1,T2,2,10
T1,T3,1,5
T1,T4,1,3
T1,T5,0,1
T2,T3,2,8