HP 48gII - Manual (Page 535)

Page 16-57
With these definitions, a general solution of Bessel’s equation for all values of
ν is given by y(x) = K
1
⋅J
ν
(x)+K
2
⋅Y
ν
(x).
In some instances, it is necessary to provide complex solutions to Bessel’s
equations by defining the Bessel functions of the third kind of order
ν as
H
n
(1) (x) = J
ν
(x)+i ⋅Y
ν
(x), and H
n
(2) (x) = J
ν
(x) −i⋅Y
ν
(x),
These functions are also known as the first and second Hankel functions of
order
ν.
In some applications you may also have to utilize the so-called modified
Bessel functions of the first kind of order
ν defined as I
ν
(x)= i - ν ⋅
J
ν
(i
⋅
x), where i is
the unit imaginary number. These functions are solutions to the differential
equation x
2 ⋅(d 2 y/dx 2 ) + x ⋅ (dy/dx)- (x 2 + ν 2 ) ⋅y = 0.
The modified Bessel functions of the second kind,
K
ν
(x) = ( π/2)⋅[I
- ν
(x) −I
ν
(x)]/sin νπ,
are also solutions of this ODE.
You can implement functions representing Bessel’s functions in the calculator
in a similar manner to that used to define Bessel’s functions of the first kind,
but keeping in mind that the infinite series in the calculator need to be
translated into a finite series.
Chebyshev or Tchebycheff polynomials
The functions T
n
(x) = cos(n ⋅cos -1 x), and U
n
(x) = sin[(n+1) cos -1 x]/(1-x 2 ) 1/2 , n
= 0, 1, … are called Chebyshev or Tchebycheff polynomials of the first and
second kind, respectively. The polynomials Tn(x) are solutions of the
differential equation (1-x
2 ) ⋅(d 2 y/dx 2 ) − x⋅ (dy/dx) + n 2 ⋅y = 0.
In the calculator the function TCHEBYCHEFF generates the Chebyshev or
Tchebycheff polynomial of the first kind of order n, given a value of n > 0. If
the integer n is negative (n < 0), the function TCHEBYCHEFF generates a
Tchebycheff polynomial of the second kind of order n whose definition is