Example use of `sparse!`

General Usage
2

If the sparsity patterns are guaranteed to always be static and identical, how about reusing the colptr and rowval vectors, as in this example:

julia> A = sprandn(10, 10, 0.05)
10×10 SparseMatrixCSC{Float64,Int64} with 5 stored entries:
  [3 ,  1]  =  -0.00762068
  [4 ,  3]  =  0.24252
  [3 ,  5]  =  -0.357867
  [3 ,  9]  =  0.451247
  [7 ,  9]  =  0.810302

julia> B = SparseMatrixCSC(size(A)..., SparseArrays.getcolptr(A), rowvals(A), rand(nnz(A)))
10×10 SparseMatrixCSC{Float64,Int64} with 5 stored entries:
  [3 ,  1]  =  0.506203
  [4 ,  3]  =  0.719589
  [3 ,  5]  =  0.336872
  [3 ,  9]  =  0.949761
  [7 ,  9]  =  0.59247