Limitation when COMPUTE_DEGREE on and PERFORM_MIRRORING off

[LorenzoPichetti]

Comment at line 614 in file normalize_graph.cu (commit 452bee8).

// NOTE: if we perform the mirroring we know that the graph is symmetric, so we can count the out degree (equal to in degree).
// if we do not perform the mirroring, either we have an undirected graph represented triangularly (i.e. if {a,b} in G then {b,a} is not in G),
// or we have a non-symmetric undirected graph. With this lines we consider that any time we do not perform the mirroring we have an undirected graph.
// This is a limitation, since the case of symmetric directed graphs (i.e. mirroring already performed in the input) and non-symmetric undirected
// graphs (i.e. exist at least a {a,b} in G s.t. {b,a} not in G and at least a {a,b} in G s.t. {b,a} in G), will produce uncorrected outputs.
// --> case 1: the degree is double
// --> case 2: ??