hello, getting the rank of a huge sparse matrix is mathematically difficult
http://math.stackexchange.com/questions/554777/rank-computation-of-large-matrices bests, M. Le lundi 16 novembre 2015 22:12:04 UTC+1, Laurent Bartholdi a écrit : > > Hello world, > I'm new at julia, and trying it out as a replacement for matlab and other > computer algebra systems. I'm a bit stuck with sparse matrices: I have > largeish matrices (10^6 x 10^6) that are very sparse, and > want to know their rank and nullspace. (the matrices decompose by blocks, > so the nullspace should be expressible as a sparse matrix). > > I tried with the latest (github) julia 0.5: > > julia> nullspace(sparse([1],[1],[1])) > ERROR: MethodError: `nullspace` has no method matching > nullspace(::SparseMatrixCSC{Int64,Int64}) > > julia> nullspace(full(sparse([1],[1],[1]))) > 1x0 Array{Float64,2} # I'm a bit unhappy here, I was hoping to get a > rational answer. > > julia> nullspace([1//1]) > 1x0 Array{Float32,2} # yikes! I'm down to 32 bits floats now. > > julia> rank(sparse([1],[1],[1.0])) > ERROR: MethodError: `svdvals!` has no method matching > svdvals!(::SparseMatrixCSC{Float64,Int64}) > > julia> rank([1.0]) > ERROR: MethodError: `rank` has no method matching rank(::Array{Float64,1}) > > julia> rank([1 0;0 1]) > 2 # finally something that works... > > Many thanks in advance! Laurent > >
