Defines the default weights matrix 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`

.- mech
A string specifying the missingness mechanism.

## Value

A matrix of size #patterns by #variables containing the weights that
will be used to calculate the weighted sum scores. Equal weights are given to
all variables. When mechanism is MAR, variables that will be amputed will be
weighted with `0`

. If it is MNAR, variables that will be observed
will be weighted with `0`

. If mechanism is MCAR, the weights matrix will
not be used. A default MAR matrix will be returned.