# pdClasses

From nlme v3.1-1

##### Positive-Definite Matrix Classes

Standard classes of positive-definite matrices (`pdMat`

)
structures available in the `nlme`

library.

- Keywords
- models

##### Value

- Available standard classes:
pdSymm general positive-definite matrix, with no additional structure pdDiag diagonal pdIdent multiple of an identity pdCompSymm compound symmetry structure (constant diagonal and constant off-diagonal elements) pdBlocked block-diagonal matrix, with diagonal blocks of any "atomic" `pdMat`

classpdNatural general positive-definite matrix in natural parametrization (i.e. parametrized in terms of standard deviations and correlations). The underlying coefficients are not unrestricted, so this class should NOT be used for optimization.

##### Note

Users may define their own `pdMat`

classes by specifying a
`constructor`

function and, at a minimum, methods for the
functions `pdConstruct`

, `pdMatrix`

and `coef`

. For
examples of these functions, see the methods for classes `pdSymm`

and `pdDiag`

.

##### See Also

*Documentation reproduced from package nlme, version 3.1-1, License: GPL version 2 or later*

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