Parametric resonance is a situation where the driving frequency is a multiple of the eigenfrequency. Various people say that using a swing and propelling it oneself is such a case, with the driving frequency being the double of the eigenfrequency. But when I use a swing, as I did today, my own motion has the same frequency as that of the swing, not twice the frequency.
An example description is http://www.hk-phy.org/articles/swing/swing_e.html which claims that self-propelled swinging is normal resonance.
The opposite is said here: Wikipedia entry
What is the correct view: is self-propelled swinging normal resonance or is it parametric resonance?