Re: [julia-users] View (a portion of a) vector as a matrix

[Tom Breloff]

Look at 'splitview' in CatViews.jl

On Sunday, October 2, 2016, 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.
>

[julia-users] View (a portion of a) vector as a matrix

[Alexey Cherkaev]

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.