R: Multiple of the Identity Positive-Definite Matrix

Multiple of the Identity Positive-Definite Matrix

Usage

pdIdent(value, form, nam, data)

Arguments

`value`	an optional initialization value, which can be any of the following: a code{pdMat} object, a positive-definite matrix, a one-sided linear formula (with variables separated by `+`), a vector of character strings, or a numeric value. Defaults to `numeric(0)`, corresponding to an uninitialized object.
`form`	an optional one-sided linear formula specifying the row/column names for the matrix represented by `object`. Because factors may be present in `form`, the formula needs to be evaluated on a data.frame to resolve the names it defines. This argument is ignored when `value` is a one-sided formula. Defaults to `NULL`.
`nam`	an optional vector of character strings specifying the row/column names for the matrix represented by object. It must have length equal to the dimension of the underlying positive-definite matrix and unreplicated elements. This argument is ignored when `value` is a vector of character strings. Defaults to `NULL`.
`data`	an optional data frame in which to evaluate the variables named in `value` and `form`. It is used to obtain the levels for `factors`, which affect the dimensions and the row/column names of the underlying matrix. If `NULL`, no attempt is made to obtain information on `factors` appearing the random effects model. Defaults to parent frame from which the function was called.

Description

This function is a constructor for the pdIdent class, representing a multiple of the identity positive-definite matrix. The matrix associated with object is represented by 1 unrestricted parameter, given by the logarithm of the square-root of the diagonal value. When value is numeric(0), an uninitialized pdMat object, a one-sided formula, or a vector of character strings, object is returned as an uninitialized pdIdent object (with just some of its attributes and its class defined) and needs to have its coefficients assigned later, generally using the coef or {matrix} functions. If value is an initialized pdMat object, object will be constructed from as.matrix(value). Finally, if value is a numeric value, it is assumed to represent the unrestricted coefficient of the underlying positive-definite matrix.

Value

a pdIdent object representing a multiple of the identity positive-definite matrix, also inheriting from class pdMat.

Author(s)

Jose Pinheiro and Douglas Bates

Examples

library(lme)
pd1 <- pdIdent(4 * diag(3), nam = c("A","B","C"))
pd1

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