findExtremaMatrix: Find local extrema in column vectors
In tdeenes/eegR: Analyze EEG Signals

findExtremaMatrix looks for local minima and maxima in the columns of a matrix. This is an internal function which supports the exported function findExtrema.

1	findExtremaMatrix(x, n, tail, constant, topN, has_NA)

`x`	a numeric matrix
`n`	the number of neighbouring points (default: 1L) to the left and to the right of each data point; a data point is a local minimum/maximum if it is below/above all data points in its neighbourhood. See also Details.
`tail`	character string defining how tails should be handled (might be abbreviated): "if_plateau" (the default) means extrema at the tails of the vector are only valid if they are part of a plateau; "never" means no extrema at the tails; "do_not_care" means no special treatment of extrema at the tails
`constant`	the value (an integer value between 0 and 3 or NA) which should be assigned to the elements of constant vectors (default: 3L)
`topN`	a positive integer scalar; if not NULL (the default), the local extrema must be among the top N highest/lowest extrema to be marked as such. If there are ties, all of them are returned.
`has_NA`	if FALSE, x is not checked for missing values, thereby speeding up the computations; if has_NA is NULL (default), a fast check is performed and if x has missing values, special corrections are applied (see Details).