rsm (version 1.40)

ccd.pick: Find a good central-composite design

Description

This function looks at all combinations of specified design parameters for central-composite designs, calculates other quantities such as the 'alpha' values for rotatability and orthogonal blocking, imposes specified restrictions, and outputs the best combinations in a order. This serves as an aid in identifying good designs. The design itself can then be generated using ccd.

Usage

ccd.pick(k, n.c = 2^k, n0.c = 1:10, blks.c = 1, n0.s = 1:10, bbr.c = 1, 
         wbr.s = 1, bbr.s = 1, best = 10, sortby = c("agreement", "N"), 
         restrict)

Arguments

k

Number of factors in the design

n.c

Number(s) of factorial points in each cube block

n0.c

Numbers(s) of center points in each cube block

blks.c

Number(s) of cube blocks that together comprise one rep of the cube portion

n0.s

Numbers(s) of center points in each star (axis-point) block

bbr.c

Number(s) of copies of each cube block

wbr.s

Number(s) of replications of each star poit within a block

bbr.s

Number(s) of copies of each star block

best

How many designs to list. Use best=NULL to list them all

sortby

String(s) containing numeric expressions that are each evaluated and used as sorting key(s). Specify sortby=NULL if no sorting is desired.

restrict

Optional string(s) containing Boolean expressions that are each evaluated. Only combinations where all expressions are TRUE are retained.

Value

• A data.frame containing best or fewer rows, and variables n.c, n0.c, blks.c, n.s, n0.s, bbr.c, wbr.s, bbr.s, N, alpha.rot, and alpha.orth, as described above.

Details

A grid is created with all combinations of n.c, n0.c, ..., bbr.s. Then for each row of the grid, several additional variables are computed: [object Object],[object Object],[object Object],[object Object],[object Object] If restrict is provided, each expression is evaluated and only the rows where the expression is TRUE are kept. (Regardless of restrict, rows are eliminated where there are insufficient degrees of freedom to estimate all needed effects for a second-order model.) The rows are sorted according to the expressions in sortby; the default is to sort by agreement and N, which is suitable for finding designs that are both rotatable and orthogonally blocked.

References

Lenth RV (2009). ``Response-Surface Methods in R, Using rsm'', Journal of Statistical Software, 32(7), 1--17. http://www.jstatsoft.org/v32/i07/. Myers, RH, Montgomery, DC, and Anderson-Cook, CM (2009), Response Surface Methodology (3rd ed.), Wiley.

See Also

ccd

Examples

library(rsm)

### List CCDs in 3 factors with between 10 and 14 runs per block
ccd.pick(3, n0.c=2:6, n0.s=2:8)
### Generate the design that is listed first.  
ccd(3, n0=c(6,4))

### Find designs in 5 factors containing 1, 2, or 4 cube blocks
### of 8 or 16 runs, 1 or 2 reps of each axis point,
### and no more than 70 runs altogether
ccd.pick(5, n.c=c(8,16), blks.c=c(1,2,4), wbr.s=1:2, restrict="N<=70")