R: Lagrange and Newtons Interpolation

newtonInterp {pracma} | R Documentation

## Lagrange and Newtons Interpolation

### Description

Lagrange's and Newton's method of polynomial interpolation.

### Usage

    newtonInterp(x, y, xs = c())

    lagrangeInterp(x, y, xs)

### Arguments

`x, y` | x-, y-coordinates of data points defining the polynomial.
`xs` | either empty, or a vector of points to be interpolated.

### Details

Straightforward implementation of Lagrange's Newton's method (vectorized in `xs`).

### Value

A vector of values at `xs` of the polynomial defined by `x,y`.

### References

Each textbook on numerical analysis.

### See Also

`neville`, `barylag`

### Examples

    p <- Poly(c(1, 2, 3))
    fp <- function(x) polyval(p, x)

    x <- 0:4; y <- fp(x)
    xx <- linspace(0, 4, 51)
    yy <- lagrangeInterp(x, y, xx)
    yy <- newtonInterp(x, y, xx)
    ## Not run:
    ezplot(fp, 0, 4)
    points(xx, yy)
    ## End(Not run)

[Package pracma version 2.0.4 Index]