# descendZero: Find start and end points of a peak In sneumann/xcms: LC-MS and GC-MS Data Analysis

 descendZero R Documentation

## Find start and end points of a peak

### Description

Decends down the sides of a data peak and finds either the points greater than or equal to the zero intercept, the intercept with a given value, or the bottom of the first valley on each side.

### Usage

```descendZero(y, istart = which.max(y))
descendValue(y, value, istart = which.max(y))
descendMin(y, istart = which.max(y))
```

### Arguments

 `y` numeric vector with values `istart` starting point for descent `value` numeric value to descend to

### Value

An integer vector of length 2 with the starting and ending indicies of the peak start and end points.

### Author(s)

Colin A. Smith, csmith@scripps.edu

`descendValue`

### Examples

```normdist <- dnorm(seq(-4, 4, .1)) - .1
xcms:::descendZero(normdist)
normdist[xcms:::descendZero(normdist)]
xcms:::descendValue(normdist, .15)
normdist[xcms:::descendValue(normdist, .15)]
xcms:::descendMin(normdist)
```

sneumann/xcms documentation built on March 18, 2023, 6:24 p.m.