Stratified Positive-Definite Matrix

DESCRIPTION:

This function is a constructor for the pdStrat class, representing a set of positive-definite matrices corresponding to different strata, defined by strata. Different pdMat classes can be used for different strata, but they must all represent matrices of equal dimensions and equal row/column names. The number of coefficients associated with this class is equal to the sum of the number of coefficients of each pdMat object it includes. 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 pdStrat 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 replacement functions.

USAGE:

pdStrat(value, form, nam, data, strata) 

REQUIRED ARGUMENTS:

value
an optional initialization value, which can be any of the following: a pdMat object, a positive-definite matrix, a one-sided linear formula (with variables separated by +), a vector of character strings, a numeric vector, or a list of pdMat objects, positive-definite matrices, or numeric vectors. If given as a list, all of its elements must represent positive-definite matrices of equal dimensions and equal row/column names, when converted to pdMat objects (in particular, all pdMat objects must have the same formula). When not given as a list, value is repeated for all strata. Defaults to numeric(0), corresponding to an uninitialized object.
form
an optional one-sided linear formula specifying the row/column names for all pdMat objects 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 matrices represented by object. It must have length equal to the dimension of the underlying positive-definite matrices 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, form, and strata. 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 in the formulas. Defaults to the parent frame from which the function was called.
strata
a one-sided formula specifying the stratification variable for the different pdMat objects represented by object. Its right hand side must evaluate to a factor or an integer in data.

VALUE:

a pdStrat object representing a set of positive-definite matrices corresponding to different strata.

SEE ALSO:

EXAMPLES:

pd1 <- pdStrat(list(pdSymm(diag(2)), pdDiag(c(1,0))), form = ~age, 
  data = Orthodont, strata = ~Sex) 
pd1