# sdellipse: Standard deviation Ellipse In phonTools: Tools for Phonetic and Acoustic Analyses

## Description

Draw standard deviation ellipses around a group of observations.

## Usage

 ```1 2``` ```sdellipse (points, stdev = 1.96, density = .01, add = TRUE, show = TRUE, means = NULL, se = FALSE, ...) ```

## Arguments

 `points` A matrix with two columns in which each row is a different observation from a bivariate normal distribution. Optionally, a 2 by 2 covariance matrix may be specified directly in conjunction with the means parameter. `stdev` The number of standard deviations to be enclosed by the ellipse. `density` The spacing between sampling points along the ellipse. A higher number results in a coarser sampling. `add` If TRUE, the ellipse is added to an existing plot. If FALSE, a new plot is created. `show ` If FALSE, no ellipse is drawn. `means` A vector of 2 means, one for each dimension. If these are specified, points is assumed to be a covariance matrix rather than a sequence of observations. `se` If TRUE, a standard error (rather than standard deviation) ellipse is plotted. `... ` Additional arguments are passed to the internal call of lines() or plot() as appropriate.

## Details

This function may be used in 2 different ways: 1) To draw standard deviation ellipses around a set of observations (if 'means' is not specified) 2) To draw ellipses and circles on plots (if 'means' is specified).

## Value

A matrix is returned where the first column indicate x-axis ellipse coordinates and the second column indicates y-axis ellipse coordinates.

## Author(s)

Santiago Barreda <sbarreda@ucdavis.edu>

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25``` ```## Examples of draws from different bivariate normal distributions ## and standard deviation ellipses drawn to fit them. par (mfrow = c(2,2)) draws = rmvtnorm (n = 1000, k = 2, sigma = .3) plot (draws) sdellipse (draws, stdev = 3, lwd = 3, col = 2) draws = rmvtnorm (n = 1000, k = 2, sigma = -.3) plot (draws) sdellipse (draws, stdev = 3, lwd = 3, col = 2) draws = rmvtnorm (n = 1000, k = 2, sigma = -.7) plot (draws) sdellipse (draws, stdev = 3, lwd = 3, col = 2) draws = rmvtnorm (n = 1000, k = 2, sigma = .7) plot (draws) sdellipse (draws, stdev = 3, lwd = 3, col = 2) ## alternatively, a covariance matrix may be specified directly. par (mfrow = c(1,1)) sdellipse (matrix(c(1,.5,.5,1),2,2), means = c(0,0), add = FALSE, stdev = 1) sdellipse (matrix(c(1,-.5,-.5,1),2,2), means = c(0,0), add = TRUE, stdev = 1) ```

### Example output  ```
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phonTools documentation built on May 1, 2019, 6:26 p.m.