RIDGE Statement
 RIDGE < options > ;
A RIDGE statement computes the ridge of optimum response.
The ridge starts at a given point x_{0},
and the point on the ridge at radius r from
x_{0} is the collection of factor settings
that optimizes the predicted response at this radius.
You can think of the ridge as climbing or falling as
fast as possible on the surface of predicted response.
Thus, the ridge analysis can be used as a tool to help
interpret an existing response surface or to indicate the
direction in which further experimentation should be performed.
The default starting point, x_{0}, has each
coordinate equal to the point midway between the
highest and lowest values of the factor in the design.
The default radii at which the ridge is
computed are 0, 0.1, ... , 0.9, 1.
If, as usual, the ridge analysis is based on the response
surface fit to coded values for the factor variables
(see the "Coding the Factor Variables" section for details), then this results
in a ridge that starts at the point with a coded zero
value for each coordinate and extends toward, but not
beyond, the edge of the range of experimentation.
Alternatively, both the center point for the ridge and
the radii at which it is to be computed can be specified.
You can specify the following options in the RIDGE statement:
 CENTER=uncodedfactorvalues

gives the coordinates of the point
x_{0} from which to begin the ridge.
The coordinates should be given in the
original (uncoded) factor variable values and should be
separated by commas.
There must be as many coordinates specified as there are
factors in the model, and the order of the coordinates
must be the same as that used in the MODEL statement.
This starting point should be well
inside the range of experimentation.
The default sets each coordinate equal to the value midway
between the highest and lowest values for the associated factor.
 MAXIMUM
 MAX

computes the ridge of maximum response.
Both the MIN and MAX options can be
specified; at least one must be specified.
 MINIMUM
 MIN

computes the ridge of minimum response.
Both the MIN and MAX options can be
specified; at least one must be specified.
 NOPRINT

suppresses the display of the ridge analysis
when only an output data set is required.
 OUTR=SASdataset

creates an output SAS data set
containing the computed optimum ridge.
For details, see the "Output Data Sets" section.
 RADIUS=codedradii

gives the distances from the ridge starting
point at which to compute the optimum.
The values in the list represent distances between coded points.
The list can take any of the following forms or can
be composed of mixtures of them:
 m_{1}, m_{2}, ... , m_{n}
 several values
 m TO n
 a sequence where m equals the starting value, n
equals the ending value, and the increment equals 1
 m TO n BY i
 a sequence where m equals the starting value, n
equals the ending value, and i equals the increment
Mixtures of the preceding forms should be separated by commas.
The default list runs from 0 to 1 by increments of 0.1.
The following are examples of valid lists.
radius=0 to 5 by .5;
radius=0, .2, .25, .3, .5 to 1.0 by .1;
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.