neutralloss {MetCirc} | R Documentation

## Calculate similarity based on neutral losses

### Description

Calculate similarity based on neutral losses (NLS)

### Usage

    neutralloss(x, y, m = 0.5, n = 2, ...)

### Arguments

`x` | 'Spectrum2' object from 'MSnbase' containing intensity and m/z values, first MS/MS spectrum
`y` | 'Spectrum2' object from 'MSnbase' containing intensity and m/z values, second MS/MS spectrum
`m` | 'numeric', exponent to calculate peak intensity-based weights
`n` | 'numeric', exponent to calculate m/z-based weights
`...` | further arguments passed to 'MSnbase:::bin_Spectra'

### Details

Similarities of spectra based on neutral losses are calculated according to the following formula:

∑(W_{S1, i} \cdot W_{S2, i}) ^ 2 ∑(W_{S1, i} ^ 2) * ∑(W_{S2, i} ^ 2)

, with W = [ peak intensity] ^{m} \cdot [ NL ]^n and NL = | m/z - precursor m/z |. For further information see Li et al. (2015): Navigating natural variation in herbivory-induced secondary metabolism in coyote tobacco populations using MS/MS structural analysis. PNAS, E4147–E4155. 'neutralloss' returns a numeric value ranging between 0 and 1, where 0 indicates no similarity between the two MS/MS features, while 1 indicates that the MS/MS features are identical. Arguments can be passed to the function 'MSnbase:::bin_Spectra', e.g. to set the width of bins (binSize). Prior to calculating

W_{S1}

or

W_{S2}

, all intensity values are divided by the maximum intensity value.

### Value

'neutralloss' returns a numeric similarity coefficient between 0 and 1

### Author(s)

Thomas Naake, thomasnaake@googlemail.com

### Examples

    data("spectra", package = "MetCirc")
    x <- spectra_tissue[[1]]
    y <- spectra_tissue[[2]]
    neutralloss(x, y, m = 0.5, n = 2, binSize = 0.01)

[Package MetCirc version 1.24.0 Index]