dispatch sparsify! on the type of matrix

Orb_AutFN.jl

@@ -34,11 +34,23 @@ immutable Settings
    tol::Float64
 end
 
-function sparsify!{T}(U::AbstractArray{T}, eps=eps(T))
-#     n = rank(U)
+function sparsify!{T}(U::Array{T}, eps=eps(T))
+    n = rank(U)
+    W = deepcopy(U)
+    W[abs.(W) .< eps] = zero(T)
+    if rank(W) != n
+        warn("Sparsification would decrease the rank!")
+        W = U
+    end
+    U = sparse(U)
+    dropzeros!(U)
+    return U
+end
+
+function sparsify!{T}(U::SparseMatrixCSC{T}, eps=eps(T))
     U[abs.(U) .< eps] = zero(T)
-#     @assert rank(U) == n
-    return sparse(U)
+    dropzeros!(U)
+    return U
 end
 
 sparsify{T}(U::AbstractArray{T}, eps=eps(T)) = sparsify!(deepcopy(U), eps)