How to use genetic algorithm optimization on a 1D nonlinear periodic electrical networks with spatially-discrete unit cells?

For the attached 1D nonlinear periodic electrical networks with spatially-discrete unit cell, how to use the genetic algorithm optimization routine available in the MATLAB Global Optimization Toolbox such that spectral power in each of the first 5 harmonics is no less than −6 dB with respect to the fundamental frequency, f = 500 MHz? I am very new to this and would appreciate any help on how to solve this problem. Thanks.

[Sam Chak]

First thing first, you need to translate this statement:

"first 5 harmonics is no less than −6 dB with respect to the fundamental frequency, f = 500 MHz"

into a form of mathematical expression (known as the Objective Function or its non-mathematical flamboyant term: Fitness Function) so that the Genetic Algorithm understands what it needs to achieve.