There should be no copy if you reshape a view.
julia> reshape((@view x[1:6]), (3, 2))
3×2
Base.ReshapedArray{Float64,2,SubArray{Float64,1,Array{Float64,1},Tuple{UnitRange{Int64}},true},Tuple{}}:
1.0 1.0
1.0 1.0
1.0 1.0
On Sunday, October 2, 2016 at 8:43:01 AM UTC-4, Alexey Cherkaev wrote:
>
> I have the model where it is convenient to represent one of the variables
> as a matrix. This variable, however, is obtained as a solution of ODEs
> (among other variables). I'm using Sundials to solve ODEs and
> `Sundials.cvode` requires the ODE RHS function to take a vector. So, it
> seems logical to pack the variables into a vector to pass to `cvode` and
> unpack them for more convenient use in my code.
>
> For example, consider `x = fill(1.0, 10)` and the first 6 entries are
> actually a matrix of size 3x2, other 4: other variables. So, I can do `s =
> reshape(x[1:6], (3,2))`. However, this creates a copy, which I would want
> to avoid. And I couldn't find a way to do the view-reshaping by applying
> `view()` function or doing `SubArray` directly. For now I settle on to
> using indices of the form `(i-1)*M + j +1` to retrieve `s[i,j] = x[(i-1)*M
> + j +1]`. But, (1) julia's 1-based arrays make it awkward to use this
> notation and (2) matrix (not element-wise) operations are not available.
>
