Defines the default relative frequency vector for the multivariate
amputation function `ampute`

.

## Arguments

- patterns
A matrix of size #patterns by #variables where

`0`

indicates a variable should have missing values and`1`

indicates a variable should remain complete. Could be the result of`ampute.default.patterns`

.

## Value

A vector of length #patterns containing the relative frequencies with which the patterns should occur. An equal probability is given to each pattern.