8 Mar 2012
**mcxmap**
12-068

mcxmap — permute or remap the indices of graphs and matrices.

**mcxmap**
**-imx** fname (*input*)

This utility relabels graphs or matrices. Its main use is in applying a
*map file* to a given matrix or graph. A map file contains a so called
*map matrix* in mcl format that has some special properties (given
further below). The functionality of mcxmap can also be provided by **mcx**, as
a mapped matrix (i.e. the result of applying a map matrix to another matrix)
is simply the usual matrix product of a matrix and a map matrix. However,
**mcx** will construct a new matrix and leave the original matrix to be mapped
alone. When dealing with huge matrices, considerable gains in efficiency
memory-wise and time-wise can be achieved by doing the mapping in-place.
This is what mcxmap does. In the future, its functionality may be
embedded in **mcx** with new mcx operators.

The special properties of a map matrix are

•

The column domain and row domain are of the same cardinality.

•

Each column has exactly one entry.

•

Each row domain index occurs in exactly one column.

These properties imply that the matrix can be used as a map from the column domain onto the row domain. An example map matrix is found in the EXAMPLES Section.

Output file.

Input file.

Different ways to specify map files.

Generate a map that maps the specified domain onto the appropriate canonical domain and write the map matrix to file.

These options have affect if neither a column map file nor column
canonification is specified. If any of the first two options is used,
column indices `i` are mapped to `a*i+b`.

These options have affect if neither a row map file nor row
canonification is specified. If any of the first two options is used,
indices `i` are mapped to `c*i+d`.

If a map file is specified for a given domain, neither a map file nor
canonification is specified. If any of the first two options is used, the
indices `i` will be mapped to `e*i+f`.

This option requires the **-map** option. **mcxmap** will output the
mapped tab definition.

The matrix below has two canonical domains which are identical. It denotes a map of the canonical domain onto itself, in which node 0 is relabeled to 8, node 1 is relabeled to 5, et cetera.

(mclheader
mcltype matrix
dimensions 12x12
)
(mclmatrix
begin
0 8 $
1 5 $
2 3 $
3 2 $
4 4 $
5 6 $
6 7 $
7 9 $
8 1 $
9 10 $
10 11 $
11 0 $
)

Stijn van Dongen.

mcxio, mcx, mcxsubs, and mclfamily for an overview of all the documentation and the utilities in the mcl family.