Hi all,

I’d like to perform an arbitrary contraction between two tensors and add the result to an existing array, without allocating an additional array. Tullio has the operation that I want, here is a simple example:

```
using Tullio
result = zeros(3, 5)
b = rand(3, 6)
c = rand(6, 5)
@tullio result[i,j] += b[i,k] * c[k, j]
```

However, my contraction expressions are generated at runtime and I can’t find a good way to produce the corresponding call to the macro from the contraction string. So, for the given example, the indices would be given in a string like “ik,kj->ij” and I’d need to call the macro using that. In the global scope I could do something like

```
using Tullio
result = zeros(3, 5)
b = rand(3, 6)
c = rand(6, 5)
exp_result = "i,j"
exp_b = "i,k"
exp_c = "k,j"
calc = "@tullio result[$exp_result] += b[$exp_b] * c[$exp_c]"
eval(Meta.parse(calc))
```

but this doesn’t work in a function and does seem like a bad idea anyway.

I understand that there are other einsum-packages for Julia, but for none of them I saw both required features (to have the += operation in place on a given array, and the acceptance of contracted axes as a parameter).

Is there a simple way to get Tullio to do what I want? Or any other package?

Help would be greatly appreciated. Thanks!