Interface functions to use `mvtnorm::rmvnorm()`

for
hyperSpec objects.

```
rmmvnorm(n, mean, sigma)
# S4 method for numeric,hyperSpec,matrix
rmmvnorm(n, mean, sigma)
# S4 method for numeric,hyperSpec,array
rmmvnorm(n, mean, sigma)
# S4 method for numeric,matrix,matrix
rmmvnorm(n, mean, sigma)
# S4 method for numeric,matrix,array
rmmvnorm(n, mean, sigma)
```

- n
vector giving the number of cases to generate for each group.

- mean
matrix with mean cases in rows.

- sigma
common covariance matrix or array (

`ncol(mean)`

x`ncol(mean)`

x`nrow(mean)`

) with individual covariance matrices for the groups.

The `mvtnorm()`

method for `hyperSpec`

objects supports producing multivariate
normal data for groups with different mean but common covariance matrix,
see the examples.

`mvtnorm::rmvnorm()`

(with 1 'm') allows a single covariance matrix.`hyperSpec::rmmvnorm()`

(with 2 'm') allows*m*ultiple covariance matrices for multiple groups. It has methods not only for`hyperSpec`

objects but also such a multi-group extension for numeric objects.

`cov()`

and `cov_pooled()`

about calculating covariance
of `hyperSpec`

objects.

```
## multiple groups, common covariance matrix
if (require("mvtnorm")) {
pcov <- cov_pooled(faux_cell, faux_cell$region)
rnd <- rmmvnorm(rep(10, 3), mean = pcov$mean, sigma = pcov$COV)
plot(rnd, col = rnd$.group)
}
#> Loading required package: mvtnorm
```