How to read data from a lookup table

Hello everyone.

I am trying to implement the standard JKR cohesion model into LIGGGHTS. I modified the equations as required in normal_force_hertz.h. For speed and efficiency reasons I created an external file (a lookup table), which provides the value of the contact radius based on the overlap distance (deltan). So with the available "deltan" value, I need to access this lookup table and interpolate the corresponding value of the contact radius. As mentioned before, I need this interpolated value of the contact radius in order to ease the calculations in normal_force_hertz.h.

Could you please advice how can I do this?

Thanks in advance!