Musical instruments that start with the letter I include the igil, ipu, Irish uillean, Irish bouzouki, ichigenkin, inci, iya, itotele and istarski mih. The instruments originate from countries ranging from Cuba and Ireland to Croatia, Japan and the Philippines.
Beno Zerr Â· ENSTA Bretagne. Bessel functions are used to solve in 3D the wave equation at a given (harmonic) frequency. The solution is generally a sum of spherical bessels functions that gives the acoustic pressure at a given location of the 3D space.
Bessel Functions are solutions of the wave equation in cylindrical and spherical coordinates, but as the previous answers have indicated, they can also be used for many other purposes with a little imagination. The classic text on them is G. N. Watson's A Treatise on the Theory of Bessel Functions.