Easing parameters

[cellcrowd]

What is the correct way of creating custom easings like you can in GSAP? It seems the library has been prepared for it as for example there is a param_s in the BACK equation class and it has a method which can set it.

public Back s(float s) {
    param_s = s;
    return this;
}

However when instantiating it, I get a 'Non-static method s(float) cannot be referenced from a static context' error.

private Back customBack = Back.s(.5f);

Tried with and without the new keyword.