Hermite's Interpolating Polynomial (original) (raw)

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Let l(x) be an nth degree polynomial with zeros at x_1, ..., x_n. Then the fundamental Hermite interpolating polynomials of the first and second kinds are defined by

 h_nu^((1))(x)=[1-(l^('')(x_nu))/(l^'(x_nu))(x-x_nu)][l_nu(x)]^2 (1)

and

 h_nu^((2))(x)=(x-x_nu)[l_nu(x)]^2 (2)

for nu=1, 2, ...n, where the fundamental polynomials of Lagrange interpolation are defined by

 l_nu(x)=(l(x))/(l^'(x_nu)(x-x_nu)). (3)

They are denoted h_nu(x) and h_nu(x), respectively, by Szegö (1975, p. 330).

These polynomials have the properties

for mu,nu=1, 2, ..., n. Now let f_1, ..., f_n and f_1^', ..., f_n^' be values. Then the expansion

 W_n(x)=sum_(nu=1)^nf_nuh_nu^((1))(x)+sum_(nu=1)^nf_nu^'h_nu^((2))(x) (8)

gives the unique Hermite interpolating fundamental polynomial for which

If f_nu^'=0, these are called Hermite's interpolating polynomials.

The fundamental polynomials satisfy

 h_1^((1))(x)+...+h_n^((1))(x)=1 (11)

and

 sum_(nu=1)^nx_nuh_nu^((1))(x)+sum_(nu=1)^nh_nu^((2))(x)=x. (12)

Also, if dalpha(x) is an arbitrary distribution on the interval [a,b], then

where lambda_nu are Christoffel numbers.


See also

Christoffel Number, Lagrange Interpolating Polynomial

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References

Bartels, R. H.; Beatty, J. C.; and Barsky, B. A. "Hermite and Cubic Spline Interpolation." Ch. 3 in An Introduction to Splines for Use in Computer Graphics and Geometric Modelling. San Francisco, CA: Morgan Kaufmann, pp. 9-17, 1998.Hildebrand, F. B. Introduction to Numerical Analysis. New York: McGraw-Hill, pp. 314-319, 1956.Szegö, G. Orthogonal Polynomials, 4th ed. Providence, RI: Amer. Math. Soc., pp. 330-332, 1975.

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Hermite's Interpolating Polynomial

Cite this as:

Weisstein, Eric W. "Hermite's Interpolating Polynomial." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/HermitesInterpolatingPolynomial.html

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