# Sum of squares and deviations Matrices

### Description

The `"SsdMatrix"`

class is the class of symmetric, dense matrices
in packed storage (just as a `dspMatrix-class`

, i.e.,
only the upper triangle is stored) defined within the `qpgraph`

package to store corrected, or uncorrected, matrices of the sum of squares
and deviations (SSD) of pairs of random variables. A corrected SSD matrix
corresponds to a sample covariance matrix.

### Objects from the Class

Objects can be created by calls of the form `new("SsdMatrix", ...)`

or by using `qpCov()`

which estimates a sample covariance
matrix from data returning an object of this class.

### Slots

`ssd`

:Object of class

`dspMatrix-class`

storing the SSD matrix.`n`

:Object of class

`"numeric"`

storing the sample size employed to estimate the SSD matrix stored in the slot`ssd`

. This is specially relevant when the SSD matrix was estimated from data with missing values by using complete observations only, which is the default mode of operation of`qpCov()`

.

### Extends

`"SsdMatrix"`

extends class `"dspMatrix"`

, directly.

### Methods

- dim
`signature(x = "SsdMatrix")`

- dimnames
`signature(x = "SsdMatrix")`

- show
`signature(object = "SsdMatrix")`

- det
`signature(object = "SsdMatrix")`

- determinant
`signature(object = "SsdMatrix", logarithm = "missing")`

- determinant
`signature(object = "SsdMatrix", logarithm = "logical")`