Welcome to the L3 Harris Geospatial documentation center. Here you will find reference guides and help documents.
﻿
>  Docs Center  >  Libraries  >  ASTROLIB  >  POLINT

POLINT

POLINT

## Purpose

Interpolate a set of N points by fitting a polynomial of degree N-1

## Explanation

Adapted from algorithm in Numerical Recipes, Press et al. (1992),
Section 3.1.

## Calling Sequence

POLINT, xa, ya, x, y, [ dy ]

## Inputs

XA - X Numeric vector, all values must be distinct. The number of
values in XA should rarely exceed 10 (i.e. a 9th order polynomial)
YA - Y Numeric vector, same number of elements
X - Numeric scalar specifying value to be interpolated

## Output

Y - Scalar, interpolated value in (XA,YA) corresponding to X

## Optional Output

DY - Error estimate on Y, scalar

## Example

Find sin(2.5) by polynomial interpolation on sin(indgen(10))
IDL> xa = indgen(10)
IDL> ya = sin( xa )
IDL> polint, xa, ya, 2.5, y ,dy

The above method gives y = .5988 & dy = 3.1e-4 a close
approximation to the actual sin(2.5) = .5985

## Method

Uses Neville's algorithm to iteratively build up the correct
polynomial, with each iteration containing one higher order.

## Revision History

Written W. Landsman January, 1992
Converted to IDL V5.0 W. Landsman September 1997

© 2022 Harris Geospatial Solutions, Inc. |  Legal