xpnd {BGLR} | R Documentation |

## Expand a Vector into a Symmetric Matrix

### Description

This function takes a vector of appropriate length (typically created using
`vech`

) and creates a symmetric matrix.

### Usage

```
xpnd(x, nrow = NULL)
```

### Arguments

`x` |
A list of elements to expand into symmetric matrix. |

`nrow` |
The number of rows (and columns) in the returned matrix. Look into the details. |

### Details

This function is particularly useful when dealing with variance covariance
matrices. Note that R stores matrices in column major order, and that the
items in `x`

will be recycled to fill the matrix if need be.

The number of rows can be specified or automatically computed from the
number of elements in a given object via ```
(-1 + \sqrt{(1 + 8 *
length(x))}) / 2
```

.

### Value

An `(nrows \times nrows)`

symmetric matrix.

### See Also

### Examples

```
xpnd(c(1,2,3,4,4,5,6,7,8,9),4)
xpnd(c(1,2,3,4,4,5,6,7,8,9))
```

[Package

*BGLR*version 1.1.2 Index]