I’m working in a problem where I have a sparse Jacobian matrix with 16 values in each row. I would like to update the matrix by just modifying its non-zero values. The problem is I would like to update both the non-zero values and indices, but the indices are immutable. How should I approach this?

# Modifying a sparse matrix non-zero indices

**bennedich**#2

You can update the `colptr`

and `rowval`

vectors directly, as in the example below, but it’s not very user friendly.

```
julia> S = sprand(3, 3, 0.25)
3×3 SparseMatrixCSC{Float64,Int64} with 2 stored entries:
[2, 1] = 0.00723938
[3, 3] = 0.9488
julia> Matrix(S)
3×3 Array{Float64,2}:
0.0 0.0 0.0
0.00723938 0.0 0.0
0.0 0.0 0.9488
julia> S.colptr
4-element Array{Int64,1}:
1
2
2
3
julia> S.rowval
2-element Array{Int64,1}:
2
3
julia> S.colptr[3] = 3; S.rowval[2] = 1;
julia> S
3×3 SparseMatrixCSC{Float64,Int64} with 2 stored entries:
[2, 1] = 0.00723938
[1, 2] = 0.9488
julia> Matrix(S)
3×3 Array{Float64,2}:
0.0 0.9488 0.0
0.00723938 0.0 0.0
0.0 0.0 0.0
```