I feel quite stupid posting this, but i can’t find a solution. I am having an array f of unknown `ndims`

(maybe 1,2,3, or even 4) and would like to access the “forward neighbors” i.e. when having an index `(i,j)`

(for the 2d case) I would like to look an `(i+1,j)`

and `(i,j+1)`

But i can’t seem to invert `ind2sub`

though there’s `sub2ind`

. In detail

```
#f = ones(20,20)
f = ones(4,4,4)
# f = ones(2,2,2,2)
for d in 1:ndims(f) # d runs over the neighbors, for each dimension one
e_d = zeros(ndims(f)); e_d[d] = 1; #in the above 2D case e_d is [1,0] or [0,1]
for i in eachindex(f)
# neighbor index
i2 = sub2ind(size(f), [sum(x) for x in zip( ind2sub(size(f), i), e_d)] ) #<--- can't get that to work, because i need single integers for sub2ind and can't get to them from the array...
a = f[i]
if (i2 <=length(f)) # i2 valid?
b = f[i2|
# continue to work with thos two and compute something say in c and d ...
c=a+b; d=a-b; #in order to let this example run for some array f; my code here is a little longer...
f[i] = c; f[i2] = d; # write back
end
end
end
```

But I can’t find a way to get back to a linear index `i2`

after adding my unit vector `e_d`

. What am I doing wrong or how can I do that? And yes I feel quite stupid, because that should be an easy task and looked for that for an hour now