Parameters in a Parametrized Data Frame
DESCRIPTION:
Returns or sets all the parameters. param returns or sets the specific parameter named in the what argument.
USAGE: 
parameters(x)
parameters(x) <- value


param(x, what)
param(x, what) <- value
REQUIRED ARGUMENTS:
x:
a data frame, specifically one inheriting from class "pframe".
OPTIONAL ARGUMENTS:
what:
character string, the name of the parameter. Parameters must be addressed by name, like attributes, which they very much resemble. This argument is required when using param.
value:
the value for the assignment.
VALUE:
parameters returns all the parameters. param returns the specific parameter named in what.
SIDE EFFECTS:
in the assignment form, parameters are changed or created. If x is not a parameterized data frame (of class "pframe") on input, then it is changed to one.

parameters replaces all the parameters, in this case value needs to be a list.

param replaces the value of the what parameter by value.

DETAILS:
Parameters are arbitrary named quantities. When a pframe object is attached or is the data argument to a model-fitting function, the parameters become available for computations just like the variables of the data frame. The names of the parameters must be unique and must not conflict with the names of the variables in the data frame.

When a data frame is given parameters with either param or parameters, it acquires the class attribute "pframe" automatically.

SEE ALSO:
nls , ms , pframe.object .
EXAMPLES: 
wafer.par <- wafer # wafer.par is a data.frame
parameters(wafer.par) <- list(a=1, b=2.3)
# wafer.par is now a pframe
parameters(wafer.par)
nls(post.mean ~ pre.mean^a + pre.dev^b, wafer.par)
param(wafer.par, "b") <- .5