Description Usage Arguments Details Value References Examples

This function defines a stratified kernel for metabolite abundance level measurements.

1 | ```
skernel(x, y, rho)
``` |

`x` |
a numerical scalar or vector of metabolomic measurements. |

`y` |
a numerical scalar or vector of metabolomic measurements. |

`rho` |
a positive kernel shape parameter. |

This function calculates a stratified kernel function *skernel* between two metabolomic measurements x and y. Suppose the metabolite-set contains *p* metabolites. Then measurements x and y have *p* components. Let *x_i* be the *i*th component of x. If *x_i=0*, then the *i*th metabolite in the metabolite-set is absent. If *x_i>0*, then the *i*th metabolite is present and *x_i* measures the abundance level of the *i*th metabolite. Measurements x and y are said to from the same stratum if they have the same set of metabolites being absent (present). If x and y are from the same stratum, then *skernel(x,y,ρ)* is assigned a Gaussian kernel with kernel parameter *ρ*. Otherwise *skernel(x,y,ρ)* is defined to be 0. More details can be found in Zhan et al. (2015).

A non-negative real value.

Zhan, X., Patterson, A. D., & Ghosh, D. (2015). Kernel approaches for differential expression analysis of mass spectrometry-based metabolomics data. BMC Bioinformatics, 16(1), 77.

1 2 3 4 5 6 |

```
[1] 0
[1] 1.125352e-07
```

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