Three-term recurrence relation for orthogonal polynomials.
roposition
(Three-term recurrence relation)
Let
be the polynomials related to measure
as in the definition (
Orthogonal
polynomials
) and the inner product
is positive definite. We
have
Proof
By definition (
Orthogonal
polynomials
)-1 ) we
have
Hence, by the proposition
(
Basic property of
orthogonal
polynomials
)
for some numbers
.
By applying the operation
to both sides for
and using orthogonality we obtain the expressions for
and
.
For
we use the
property
and orthogonality to
find
Definition
(Jacobi matrix) We introduce the following notation
1.
2. The numbers
are zeros of
:
for each
.
Proposition
(Zeros of orthogonal polynomials)
Let
be the polynomials related to measure
as in the definition (
Orthogonal
polynomials
)-2 and the inner product
is positive definite. The zeros
are eigenvalues of the matrix
for each
and
are the corresponding eigenvectors.
Proof
The proposition (
Three-term
recurrence relation
) main statement
is
and may be rewritten as
We
substitute
then
We divide the last relationship by
then
or
We restate the last result in matrix form as
where
and
.
The statement is apparent after the substitution
.