Detecting symmetry in Market fromats

[maawad]

Is your feature request related to a problem? Please describe.
Some Matrix Market files may be symmetric but the entire graph is stored in the file. Algorithms that require a symmetric input graph will not be able to detect that. Currently, we do this check in algorithms that require symmetric input (e.g., in TC):

io::matrix_market_t<vertex_t, edge_t, weight_t> mm;
auto mmatrix = mm.load(filename_);
if (!mm_is_symmetric(mm.code)) {
  std::cerr << "Error: input matrix must be symmetric" << std::endl;
  exit(1);
}

Describe the solution you'd like
Detect if the graph is symmetric after reading the general input Matrix Market file

[neoblizz]

Detect if the graph is symmetric after reading the general input Matrix Market file

Do you mean not rely on the header of the MTX?

[maawad]

The header contains the keyword "general" instead of "symmetric". Here is an example:

%%MatrixMarket matrix coordinate pattern symmetric
% kind: undirected random graph
4194304 4194304 30359198

is the same graph as:

%%MatrixMarket matrix coordinate real general
4194304 4194304 60718396

[neoblizz]

Ok, I understand. Old gunrock got around this problem by allowing an option to "make undirected", which will first remove all the self-loops and then add a duplicate for every edge. It is not the same as "detecting" symmetry but will work the same way in practice. If I get some time, I'll consider adding this as a graph tool: https://github.com/gunrock/essentials/blob/master/include/gunrock/graph/graph.hxx#L405