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A [[Quadrature formula of highest algebraic accuracy|quadrature formula of highest algebraic accuracy]] of the type

\begin{equation*} \int _ { a } ^ { b } p ( x ) f ( x ) d x \approx Q _ { 2 ^ {i}  ( n + 1 ) - 1 } [ f ] = \end{equation*}

\begin{equation*} = \sum _ { \nu = 1 } ^ { n } \alpha _ { i \nu }\, f ( x _ { \nu } ) + \sum _ { \rho = 1 } ^ { i } \sum _ { \nu = 1 } ^ { 2 ^ { \rho - 1 } ( n + 1 ) } \beta _ { i \rho \nu }\, f ( \xi _ { \nu } ^ { \rho } ), \end{equation*}

$i \geq 1$, where $x _ { 1 } , \ldots , x _ { n }$ are the nodes of a [[Gauss quadrature formula|Gauss quadrature formula]] and the nodes of $Q _ { 2 ^{ i - 1} ( n + 1 ) - 1 }$ are fixed in the construction of $Q _ { 2 ^{ i}  ( n + 1 ) - 1 }$ [[#References|[a2]]]. Nested sequences of Kronrod–Patterson formulas are used for the numerical approximation of definite integrals with practical error estimate, in particular in the non-adaptive routines of the numerical integration package QUADPACK [[#References|[a4]]] and in the standard numerical software libraries.

The algebraic accuracy of $Q _ { 2 ^{ i}  ( n + 1 ) - 1 }$ is at least $3.2 ^ { i - 1 } ( n + 1 ) - 2$. The free nodes $\xi _ { 1 } ^ { i } , \ldots , \xi _ { 2 ^ { i - 1 } ( n + 1 ) } ^ { i } $ of $Q _ { 2 ^{ i}  ( n + 1 ) - 1 }$ are precisely the zeros of the polynomial $E _ { 2 ^{i-1}(n+1)} ^ { i } $ which satisfies

$$
\int_a^b p(x) P_n(x) \prod_{\rho=1}^i E_{2^{\rho-1}(n+1)}^\rho (x) x^k \, dx = 0,
$$

\begin{equation*} k = 0 , \ldots , 2 ^ { i - 1 } ( n + 1 ) - 1, \end{equation*}

where $\{ P _ { n } \}$ is the system of [[Orthogonal polynomials|orthogonal polynomials]] associated with $p$, $Q _ { 2 n+1} $ is the [[Gauss–Kronrod quadrature formula|Gauss–Kronrod quadrature formula]], and $E _ { n + 1 } ^ { 1 }$ is the Stieltjes polynomial (cf. [[Stieltjes polynomials|Stieltjes polynomials]]). For $[ a , b ] = [ - 1,1 ]$ and $p ( x ) = \sqrt { 1 - x ^ { 2 } }$, $P _ { n } = U _ { n }$, the Chebyshev polynomial of the second kind (cf. [[Chebyshev polynomials|Chebyshev polynomials]]), and $E  ^{ i } _ { 2 ^{ i - 1}  ( n + 1 ) } = T _ { 2 ^{ i - 1}  ( n + 1 ) }$, the Chebyshev polynomial of the first kind. In this case, all Kronrod–Patterson formulas are Gauss quadrature formulas (cf. [[Gauss quadrature formula|Gauss quadrature formula]]). Hence, the algebraic accuracy of $Q _ { 2 ^{ i}  ( n + 1 ) - 1 }$ is $2 ^ { i + 1 } ( n + 1 ) - 3$, the nodes of $Q _ { 2 ^{ i - 1} ( n + 1 ) - 1 }$ and $Q _ { 2 ^{ i}  ( n + 1 ) - 1 }$ interlace and the formulas have positive weights. Similar properties are known for the more general Bernstein–Szegö weight functions $p ( x ) = \sqrt { 1 - x ^ { 2 } } / \rho _ { m } ( x )$, where $\rho _ { m }$ is a polynomial of degree $m$ which is positive on $[ a , b ] = [ - 1,1 ]$, see [[#References|[a3]]].

Only very little is known for $p \equiv 1$, which is the most important case for practical calculations. Tables of sequences of Kronrod–Patterson formulas have been given in [[#References|[a2]]], [[#References|[a4]]]. A numerical investigation for $ i  = 2$ and Jacobi weight functions $p ( x ) = ( 1 - x ) ^ { \alpha } ( 1 + x ) ^ { \beta }$, $\alpha , \beta &gt; - 1$, can be found in [[#References|[a5]]].

====References====
<table><tr><td valign="top">[a1]</td> <td valign="top">  P.J. Davis,   P. Rabinowitz,   "Methods of numerical integration" , Acad. Press  (1984)  (Edition: Second)</td></tr><tr><td valign="top">[a2]</td> <td valign="top">  T.N.L. Patterson,   "The optimum addition of points to quadrature formulae"  ''Math. Comput.'' , '''22'''  (1968)  pp. 847–856</td></tr><tr><td valign="top">[a3]</td> <td valign="top">  F. Peherstorfer,   "Weight functions admitting repeated positive Kronrod quadrature"  ''BIT'' , '''30'''  (1990)  pp. 241–251</td></tr><tr><td valign="top">[a4]</td> <td valign="top">  R. Piessens,   et al.,   "QUADPACK: a subroutine package in automatic integration" , Springer  (1983)</td></tr><tr><td valign="top">[a5]</td> <td valign="top">  P. Rabinowitz,   S. Elhay,   J. Kautsky,   "Empirical mathematics: the first Patterson extension of Gauss–Kronrod rules"  ''Internat. J. Computer Math.'' , '''36'''  (1990)  pp. 119–129</td></tr></table>