Legendre rational functions

Plot of the Legendre rational functions for n=0,1,2 and 3 for x between 0.01 and 100.

In mathematics the Legendre rational functions are a sequence of orthogonal functions on [0, ∞). They are obtained by composing the Cayley transform with Legendre polynomials.

A rational Legendre function of degree n is defined as:

where is a Legendre polynomial. These functions are eigenfunctions of the singular Sturm-Liouville problem:

with eigenvalues

PropertiesEdit

Many properties can be derived from the properties of the Legendre polynomials of the first kind. Other properties are unique to the functions themselves.

RecursionEdit

 

and

 

Limiting behaviorEdit

 
Plot of the seventh order (n=7) Legendre rational function multiplied by 1+x for x between 0.01 and 100. Note that there are n zeroes arranged symmetrically about x=1 and if x0 is a zero, then 1/x0 is a zero as well. These properties hold for all orders.

It can be shown that

 

and

 

OrthogonalityEdit

 

where   is the Kronecker delta function.

Particular valuesEdit

 
 
 
 
 

ReferencesEdit

Zhong-Qing, Wang; Ben-Yu, Guo (2005). "A mixed spectral method for incompressible viscous fluid flow in an infinite strip". Mat. Apl. Comput. 24 (3). doi:10.1590/S0101-82052005000300002.