Output permutation in einsum fails

[matthiasneuner]

Hello Roman,

your snippet regarding OIndex in einsum from the Wiki does not compile for me:

enum {I,J,K,L,M,N};

Tensor<double,2,3,5> A; Tensor<double,3,5,2,4> B;
// fill A and B
A.random(); B.random();
// Order as I,K,L,M,N - same as default
auto C = einsum<Index<I,J,K>,Index<J,L,M,N>,OIndex<I,K,L,M,N>>(A,B);    // works

// Order as I,L,K,N,M - resulting tensor [Tensor<double,2,5,5,4,2>]
auto D = einsum<Index<I,J,K>,Index<J,L,M,N>,OIndex<I,M,K,N,M>>(A,B);    // fails

Although using OIndex works in many places, occasionally it fails to compile, like in the example above.
Thank you in advance :-) !

[romeric]

The Wiki entry is incorrect. In the second example, there are duplicate entries in the output Index (in OIndex<I,M,K,N,M>, M is repeated twice).

There is some discussion on how to support this feature, see #91. In the above example however, even if the duplicate entries were taken care of the output tensor cannot be reshaped like that. That typo makes the whole example incorrect. I will correct the Wiki. If you have other cases where einsum with OIndex fails, report it.