The control function may fully determine the time-dependent form of the
external field, or only the envelope function of this external field, or its phase.
Or, we may have two different control functions, one of them providing the phase
and the other one, the envelope.
Note that, if OCTControlRepresentation = control_function_real_time, then the control
function must always determine the full external field (THIS NEEDS TO BE FIXED).
In this case, the control function determines the full control function: namely,
if we are considering the electric field of a laser, the time-dependent electric field.
The optimization process attempts to find the best possible envelope. The full
control field is this envelope times a cosine function with a "carrier" frequency.
This carrier frequency is given by the carrier frequency of the TDExternalFields
in the inp file.