Add Center Points to a Fractional Factorial Design
DESCRIPTION:
This function is primarily a utility used by design.digest.
USAGE:
addcp(x, n.cp, cp.values, cp.place)
REQUIRED ARGUMENTS:
See design.digest for a description of the arguments.
VALUE:
A fac.design object, with center points added as requested. A "hidden"
(i.e. non-printing) factor Quad is added to the design if there are
center points, that is used
by fac.aov to fit a quadratic term to the center points.
DETAILS:
The contrasts of the returned fac.design are specified in the returned
design. They are set so that the center points are used to estimate a
quadratic effect of center points versus design points, via the "dummy"
factor Quad. In addition, the contrasts are set so that every
estimated terms in the model fit by the default formula(x) has equal
standard error.