Description
openedon Jun 15, 2017
The documentation for the spones function describes the Matlab behavior for this function, which replaces each non-zero entry by a value of 1.0. However, the implementation appears to use julia's notion of "stored entries" instead.
julia> versioninfo()
Julia Version 0.6.0-rc3.0
Commit ad290e9 (2017-06-07 11:53 UTC)
Platform Info:
OS: Linux (x86_64-pc-linux-gnu)
CPU: Intel(R) Xeon(R) CPU E5-1650 v3 @ 3.50GHz
WORD_SIZE: 64
BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Haswell)
LAPACK: libopenblas64_
LIBM: libopenlibm
LLVM: libLLVM-3.9.1 (ORCJIT, haswell)
help?> spones
search: spones unsafe_pointer_to_objref
spones(S)
Create a sparse array with the same structure as that of S, but with every nonzero element having the value 1.0.
julia> A = sparse([1,2,3,4],[2,4,3,1],[5.,4.,3.,2.])
4×4 SparseMatrixCSC{Float64,Int64} with 4 stored entries:
[4, 1] = 2.0
[1, 2] = 5.0
[3, 3] = 3.0
[2, 4] = 4.0
julia> spones(A)
4×4 SparseMatrixCSC{Float64,Int64} with 4 stored entries:
[4, 1] = 1.0
[1, 2] = 1.0
[3, 3] = 1.0
[2, 4] = 1.0
Note the difference from speye.
julia> A = sparse([1,2],[1,2],[true,false])
2×2 SparseMatrixCSC{Bool,Int64} with 2 stored entries:
[1, 1] = true
[2, 2] = false
julia> B = spones(A)
2×2 SparseMatrixCSC{Bool,Int64} with 2 stored entries:
[1, 1] = true
[2, 2] = true
julia> A = sparse([1,2],[1,2],[1.0,0.0])
2×2 SparseMatrixCSC{Float64,Int64} with 2 stored entries:
[1, 1] = 1.0
[2, 2] = 0.0
julia> C = spones(A)
2×2 SparseMatrixCSC{Float64,Int64} with 2 stored entries:
[1, 1] = 1.0
[2, 2] = 1.0
Expected behavior given the documentation
julia> B = spones(A)
2×2 SparseMatrixCSC{Float64,Int64} with 1 stored entries:
[1, 1] = 1.0
julia> C = spones(A)
2×2 SparseMatrixCSC{Float64,Int64} with 1 stored entries:
[1, 1] = 1.0
So note that there are two issues with the current documentation. First, the value is one(T) not 1.0. Second, the operation proceeds over the stored entries, not the non-zero stored entries.
Ideal handling.
- Change the operation of
sponesto do the same thing as Matlab's function. In which case, this would operate according to the documentation. (That is, it would satisfy the relationshipcountnz(spones(A)) == countnz(A)) - Introduce a new function for the current behavior.
spsones?
Minimal handling.
- Adjust the documentation for the current function. Would suggest including an example describing the difference from Matlab's behavior (as above).
I don't like the minimal handling because the semantics of Matlab's spones and Julia's spones are radically different in unexpected and bug-inducing fashions because I have no idea which Julia operations introduce new structural non-zeros. (Let's just say I spent a while working with the wrong distribution of random matrices.)