# getBlocks

0th

Percentile

##### Get Blocks of a Graph

Obtain blocks of vertices of a 1D, 2D, or 3D graph, in order to use the conditional independence to speed up the simulation (checkerboard idea).

Keywords
spatial
##### Usage
getBlocks(mask, nblock)
##### Arguments
a vector, matrix, or 3D array specifying vertices of a graph. Vertices of value 1 are within the graph and 0 are not.
nblock
a scalar specifying the number of blocks. Right now, for a 2D graph nblock could be either 2 or 4, and for a 3D graph nblock could be either 2 or 8.
##### Details

The vertices within each block are mutually independent given the vertices in other blocks. Some blocks could be empty.

##### Value

• A list with the number of components equal to nblock. Each component consists of vertices within the same block.

##### References

Darren J. Wilkinson Parallel Bayesian Computation Handbook of Parallel Computing and Statistics 481-512 Marcel Dekker/CRC Press 2005

• getBlocks
##### Examples
#Example 1: split a line into 2 blocks

#Example 2: split a \eqn{4 \times 4} 2D graph into 4 blocks in order
#           to use the checkerboard idea for a neighborhood structure
#           corresponding to the second-order Markov random field.
getBlocks(mask, nblock=8)