thumb|right|200px|One of the possible modes of vibration of an idealized circular drum head. These modes are eigenfunctions of a linear operator on a function space, a common construction in functional analysis.
th?umb|right|200px|One of the possible modes of vibration of an idealized circular drum head. Thes,e mod,es are eigenfunctions of a linear operator on a, function space, a common construction in function,al analysis.