projector {dae} | R Documentation |

## Create projectors

### Description

The class "`projector`

" is the
subclass of the class "`matrix`

"
in which matrices are square, symmetric and idempotent.

The function `projector`

tests whether a `matrix`

satisfies these criteria and if it does creates a
"`projector`

" object, computing the
projector's degrees of freedom and adding them to the object.

### Usage

`projector(Q)`

### Arguments

`Q` |
The |

### Details

In checking that the `matrix`

is square, symmetric and
idempotent, the equality of the `matrix`

with either its
transpose or square is tested. In this, a difference in elements is
considered to be zero if it is less than `daeTolerance`

, which is
initially set to `.Machine$double.eps ^ 0.5`

(about 1.5E-08).
The function `set.daeTolerance`

can
be used to change `daeTolerance`

.

### Value

An object of Class "`projector`

" that
consists of a square, summetric, idempotent `matrix`

and
degrees of freedom (rank) of the `matrix.`

### Author(s)

Chris Brien

### See Also

`degfree`

, `correct.degfree`

in package dae.

`projector`

for further information about this class.

### Examples

```
## set up a 2 x 2 mean operator that takes the mean of a vector of 2 values
m <- matrix(rep(0.5,4), nrow=2)
## create an object of class projector
proj.m <- projector(m)
## check that it is a valid projector
is.projector(proj.m)
```

*dae*version 3.2.28 Index]