# pchip: Piecewise cubic hermite interpolation In signal: Signal Processing

## Description

Piecewise cubic hermite interpolation.

## Usage

 1 pchip(x, y, xi = NULL)

## Arguments

 x,y vectors giving the coordinates of the points to be interpolated. x must be strictly monotonic (either increasing or decreasing). xi points at which to interpolate.

## Details

In contrast to spline, pchip preserves the monotonicity of x and y.

## Value

Normally, the interpolated signal, an array of length(xi).

if xi == NULL, a list of class pp, a piecewise polynomial representation with the following elements:

 x breaks between intervals. P a matrix with n times d rows and k columns. The ith row of P, P[i,], contains the coefficients for the polynomial over the ith interval, ordered from highest to lowest. There must be one row for each interval in x. n number of intervals (length(x) - 1). k polynomial order. d number of polynomials.

## Author(s)

Original Octave version by Paul Kienzle pkienzle@user.sf.net. Conversion to R by Tom Short.

## References

Fritsch, F. N. and Carlson, R. E., “Monotone Piecewise Cubic Interpolation”, SIAM Journal on Numerical Analysis, vol. 17, pp. 238-246, 1980.

Octave Forge https://octave.sourceforge.io/

## Examples

 1 2 3 4 5 6 7 xf <- seq(0, 11, length=500) yf <- sin(2*pi*xf/5) xp <- c(0:10) yp <- sin(2*pi*xp/5) pch <- pchip(xp, yp, xf) plot(xp, yp, xlim = c(0, 11)) lines(xf, pch, col = "orange")

### Example output

Attaching package: 'signal'

The following objects are masked from 'package:stats':

filter, poly

signal documentation built on May 25, 2021, 9:06 a.m.