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### rmat2 command

Syntax:

```rmat N Nz a b c d fraction seed -o out1.file out1.mr
rmat2 N Nz a b c d fraction seed -o out1.file out1.mr
```
• N = order of matrix, 2^N = number of rows in matrix
• Nz = average # of non-zeroes per row, Nz * 2^N = total # of non-zeroes
• a,b,c,d = R-MAT parameters which sum to 1.0
• fraction = R-MAT twiddle factor
• seed = random number seed (positive integer)
• out1 = graph edges: Key = Vi Vj, Value = NULL

Examples:

```rmat 20 8 0.45 0.25 0.25 0.05 0.0 284958 -o NULL mre
rmat2 20 8 0.45 0.25 0.25 0.05 0.0 284958 -o tmp.rmat NULL
```

Description:

These are named commands which generate a sparse random matrix via the procedure defined for R-MAT matrices, as discussed in the paper by (Chakrabarti). Such matrices are often used to represent graphs where the vertices are numbered 1 to Nrows, and the non-zero matrix entries represent edges. The number of rows and non-zero entries are determined by the specified N and Nz arguments.

Depending on the choice of the R-MAT parameters the degree distribution of the resulting graph can be roughly uniform or highly skewed, which is useful in modeling different kind of graphs, e.g. Internet connectivity. The a,b,c,d parameters must sum to 1.0 and represent weighting for the 4 different quadrants of the matrix. As non-zero entries are generated, they are assigned to each quadrant in a recursive manner using the a,b,c,d weightings and a random number generator. A fraction value of 0.0 means the a,b,c,d weightings are used as-is. A fraction value > 0.0 but < 1.0 means the weightings are randomly twiddled at each iteration of the recursion.

The MapReduce algorithms used for performing the R-MAT generation are described in the paper by (Plimpton). The rmat command implements the first of the two algorithms discussed in the paper. The rmat2 command implements the second of the two algorithms.

See the named command doc page for various ways in which the -i inputs and -o outputs for a named command can be specified.

These commands take no inputs.

Out1 will store the list of edges of the R-MAT graph, or equivalently, the I,J indices of non-zeroes in the matrix. There will be exactly Nz * 2^N entries in out1. This may include some duplicate or self-edges. A duplicate edge is when both (Vi,Vj) or (Vj,Vi) appear. A self-edge is when (Vi,Vi) appears. If desired, these can be removed by further processing; see the edge_upper command.

Related commands:

(Chakrabarti) Chakrabarti, Zhan, Faloutsos, "R-MAT: A recursive model for graph mining", in SIAM Data Mining (2004).

(Plimpton) Plimpton and Devine, "MapReduce in MPI for Large-Scale Graph Algorithms", to appear in Parallel Computing (2011).