Summing columns of an array in Julia gives an error-CodePudding

In my Julia optimisation model, I have a variable A which is a 5x5x5 array. Then A[:,:,1] is a matrix. In my model, I wish to calculate the sum of the column vectors of A[:,:,1]. Here is my code:

I = 1:5; J = 1:5; K = 1:5;

m = Model(HiGHS.Optimizer)
@variable(m, A[i in I, j in J, t in K] >= 0)

sum(A[:,:,1],dims = 2)

However, this gives me an error:

No method is implemented for reducing index range of type UnitRange{Int64}. Please implement reduced_index for this index type or report this as an issue.

How can I fix this error? The code works if I write

@variable(m, A[i in 1:5, j in 1:5, t in 1:5] >= 0)

but in my model, the indices I, J and K are given as an input to a function, so I cannot specify them like that.

CodePudding user response：

A[:,:,1] yields a 2-dimensional DenseAxisArray. You should do collect on it to be able to aggregate via sum(..., dims=...). Hence you need to do:

julia> sum(collect(A[:,:,1]),dims = 2)
5×1 Matrix{AffExpr}:
 A[1,1,1]   A[1,2,1]   A[1,3,1]   A[1,4,1]   A[1,5,1]
 A[2,1,1]   A[2,2,1]   A[2,3,1]   A[2,4,1]   A[2,5,1]
 A[3,1,1]   A[3,2,1]   A[3,3,1]   A[3,4,1]   A[3,5,1]
 A[4,1,1]   A[4,2,1]   A[4,3,1]   A[4,4,1]   A[4,5,1]
 A[5,1,1]   A[5,2,1]   A[5,3,1]   A[5,4,1]   A[5,5,1]

Please also note that your variable definition can be shortened to @variable(m, A[I, J, K] >= 0)