fac.sumop {dae} | R Documentation |

## computes the summation matrix that produces sums corresponding to a (generalized) factor

### Description

Computes the matrix that produces the sums
corresponding to a (generalized) `factor`

.

### Usage

`fac.sumop(factor)`

### Arguments

`factor` |
The (generalized) |

### Details

The design matrix **X** for a (generalized) `factor`

is formed with a
column for each `level`

of the (generalized) `factor`

, this column
being its indicator variable. The summation matrix is formed as
`X %*% t(X)`

.

A generalized `factor`

is a `factor`

formed from the combinations of
the `levels`

of several original `factors`

. Generalized `factors`

can be formed using `fac.combine`

.

### Value

A symmetric matrix.

### Author(s)

Chris Brien

### See Also

`fac.combine`

, `fac.meanop`

in package dae.

### Examples

```
## set up a two-level factoir and a three-level factor, both of length 12
A <- factor(rep(1:2, each=6))
B <- factor(rep(1:3, each=2, times=2))
## create a generlaized factor whose levels are the combinations of A and B
AB <- fac.combine(list(A,B))
## obtain the operator that computes the AB means from a vector of length 12
S.AB <- fac.sumop(AB)
```

[Package

*dae*version 3.2.28 Index]