Construct a Grid Suitable for Contour Plots

DESCRIPTION:

Construct a grid of factor settings (x, y) and predicted response (z) values from a response surface fit.

This is a support function for contour.rsm.lm, surface.rsm.lm and image.rsm.lm .

USAGE:

grid(rsm.object, gran, vary) 

REQUIRED ARGUMENTS:

rsm.object
the output from fitting a response surface using rsm.lm.
gran
length of the vectors containing the x and y coordinates of the grid over which the response is evaluated.
vary
a list, with components named by the factors in rsm.object, that determines which two factors are varied on the x and y axes while the remaining factors are held constant. The components corresponding to the factors to be varied are assigned the value "v", while the remaining components are assigned either an explicit numeric value or the value "c" to indicate that the factor is to be held constant at its center point. (If a variable is omitted from the list, "c" is assumed.) By default, the first two factors in rsm.object are varied.

VALUE:

A list containing the following components:
x,y
the factor values over which the grid is constructed.
z
a vector of predicted response values at the factor settings (x,y).
xname
name for the x factor.
yname
name for the y factor.
hold.names
names for any other factors in the model which are held fixed.
hold.values
values at which the other factors are held fixed.

DETAILS:

this function is called by surface.rsm.lm, contour.rsm.lm and image.rsm.lm .

SEE ALSO:

, , , , , .