Hello,
Here is the equation of an anharmonic oscillator; For example, a mass m fixed to a special spring is considered here:
$$m \frac{d^2 x}{dt^2}- K x+AKx^3=0$$
I want to modify this equation to insert 50 cycles of the round trip of the mass in one second.
How to write this sequel? (I do not know where and what value to modify)
Thank you

There are no particles, there are only fields