DRAFT: gnuplot: Cosine oscillating on arbitrary function

To let a cosine oscillate on an "arbitrary" function, when the function goes up the x coordinate might go backwards, so we can't express this as a single-valued function from x to y. But we can use parametric curves, instead; they go from a separate parameter, t, to points (x(t), y(t)). (In gnuplot, this is set parametric.)

As starter, here is what the final result will look like for cosine oscillating on cosine:
gnuplot result of cosine on cosine
(gnuplot source code of cosine on cosine)
This is what motivated myself to write up a blog post about the topic.