## Introduction

Cyclic incomplete block designs (IBDs) are IBDs generated by the cyclic
development of one or more suitably chosen initial blocks. Cyclic IBDs accounts
for a large number of balanced IBDs or BIBDs in Fisher & Yates (1963) and
Rao (1961). They also provide efficient alternatives to many partially balanced
IBDs, or PBIBDs, catalogued in Clatworthy (1973). Chapter 3 of John &
Williams (1995) gives an excellent summary of cyclic designs. In this note this
book is abbreviated as JW. When the number of replications *r* is equal to
or is a multiple of the block size *k*, cyclic IBDs render automatic
elimination of heterogeneity in two directions (see Section 5.7 of JW). Being an important class of IBD, cyclic IBDs have been
extensively catalogued by John *et al.* (1972).

CIBD is a Gendex module for generating optimal or near-optimal cyclic IBDs. CIBD can handle up to 10,000 treatments. Designs constructed by CIBD can be used as column components of row-column designs (see Nguyen 1997). CIBD uses a 2-stage optimization process. Each stage of the optimization process uses an algorithm similar to the cyclic-coordinate exchange algorithm described in Nguyen (2002). The detailed account of the CIBD algorithm will be given elsewhere.

## Using CIBD

Let's assume all Gendex class files are in the directory c:\gendex and
suppose you want to construct a cyclic IBD of size (*v,k,r*)=(6,2,4). At
the working directory, type the following command at the Command Prompt (case
is important):

java -cp c:\gendex CIBD

The CIBD window will pop up. Enter the values 6, 2 and 4 in the
(*v,k,r*) combination fields, the CIBD window will become:

Now click **START**, the following window will pop up:

You encounter this question when the number of replications *r* is
equal to or is a multiple of the block size *k*. The order of blocks
generated by the same initial block and the order of treatments within blocks
are always randomized. Answering Yes to this question if you do not want to
randomize the treatments within blocks (you want to construct a Youden square
type design). Now click **Yes**, CIBD will start running and after try 1,
the plan of the constructed design for this try pops up in the CIBD output window
(as the ratio *E/U* reaches 1) and CIBD stops::

The

**START**button has changed to

**RESET**button. If you click this

**RESET**button, the output will disappear and you can use CIBD for a new design problem. Note that the default random seed is the one obtained from the system clock and the default number of tries is 100. You can change these default values if you wish to.

## Output

The result of the best try is displayed in the CIBD output window and is also saved in the file CIBD.htm in the working directory. This
file can be read by a browser such as IE or *Google Chrome*. Information for
this try includes:

- Try number;
- The number of iterations;
*E*, the efficiency factor of this design;- The ratio
*E/U*where*U*is the upper bound of an IBD.*U*=*U*where_{J}*U*is the bound of Jarrett (1989) good for any regular graph design (RGD). An RGD is an IBD with concurrences differing by at most 1. The program automatically stops if this ratio reaches 1._{J} - The distribution of the concurrences of this design;
- The design plan and the associated initial block(s) and random seed;
- The time in seconds CIBD used to construct this design;

An additional output of a CIBD session is the file form.htm. This file contains the randomized plan of the constructed design.

## Examples

- A cyclic IBD of size (
*v,k,r*)=(7,3,15) (http://designcomputing.net/gendex/cibd/c1.html). - A cyclic IBD of size (
*v,k,r*)=(8,4,35) (http://designcomputing.net/gendex/cibd/c2.html). - A cyclic IBD of size (
*v,k,r*)=(11,4,4) (http://designcomputing.net/gendex/cibd/c3.html). - A cyclic IBD of size (
*v,k,r*)=(8,4,6) (http://designcomputing.net/gendex/cibd/c4.html). - A cyclic IBD of size (
*v,k,r*)=(12,4,6) (http://designcomputing.net/gendex/cibd/c5.html). - A cyclic IBD of size (
*v,k,r*)=(12,4,8) (http://designcomputing.net/gendex/cibd/c6.html). - A cyclic IBD of size (
*v,k,r*)=(15,4,4) (http://designcomputing.net/gendex/cibd/c7.html). - A cyclic IBD of size (
*v,k,r*)=(91,10,10) (http://designcomputing.net/gendex/cibd/c8.html). - A cyclic IBD of size (
*v,k,r*)=(133,12,12) (http://designcomputing.net/gendex/cibd/c9.html). - A cyclic IBD of size (
*v,k,r*)=(183,14,14) (http://designcomputing.net/gendex/cibd/c10.html). - A cyclic IBD of size (
*v,k,r*)=(43,7,14) (http://designcomputing.net/gendex/cibd/c11.html). - A cyclic IBD of size (
*v,k,r*)=(61,5,15) (http://designcomputing.net/gendex/cibd/c12.html).

**Notes**:

- Example 1: See the example in JW Section 3.2.
- Example 2. See the example in JW Section 3.2.
- Example 3: See JW Example 3.1.
- Example 4: See the example in JW Section 3.4.
- Example 5: See the example in JW Section 3.4.
- Example 6: See the example in JW Section 3.4.
- Example 4, 7-12: The constructed IBDs are also of Youden square type designs.

## References

Clatworthy, W.H. (1973) *Tables of two-associates- class partially
balanced designs*. Applied. Math. Ser. 63. National Bureau of Standards,
Washington.

Fisher, R.A. & Yates, F. (1963) *Statistical tables for biological,
agricultural and medical research*. London: Oliver & Boyd.

Jarrett, R.G. (1989). A review of bounds for the efficiency factor of block
designs. *Austral. J. Statist.* **31**, 118-129.

John, J.A. & Williams E.R. (1995) *Cyclic designs and computer-generated
designs*. New York: Chapman & Hall.

John, J.A., Wolock, F.W. & David, H.A. (1972) *Cyclic Designs*.
Applied. Math. Ser. 62. National Bureau of Standards, Washington.

Nguyen, N-K (2001) A modified cyclic-coordinate exchange algorithm as
illustrated by the construction of minimum-point second-order designs.
*Advances in Statistics, Combinatorics and Related Areas.* Edited by C.
Gulati, Y-X Lin, S. Mishra, J. Rayner. World Scientific Publishing Co. Pte.
Ltd., 205-210.

Nguyen, N-K. and Williams, E.R. (1993) An algorithm for constructing optimal
resolvable row-column designs. *Austral. J. Statist.* **35**,
363-370.

Patterson, H.D. & Williams, E.R. (1976a) A new class of resolvable
incomplete block designs. *Biometrika* **63**, 83-92.

Patterson, H.D. & Williams, E.R. (1976b) Some theoretical results on
general block designs. *In Proceedings of the 5th British Combinatorial
Conference*. Congressus Numeratium XV, 489-496, Utilitas Mathematica,
Winnipeg.

Rao, C.R. (1961) A study of BIB design with replication 11 to 15. *Sankhya
A* **23**, 117-127.

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