[GitHub] jasonyu1996 opened a new issue #12327: [Feature Request] support of diag for N-d arrays

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jasonyu1996 opened a new issue #12327: [Feature Request] support of diag for N-d arrays
URL: https://github.com/apache/incubator-mxnet/issues/12327
 
 
   Hi! 
   
   I just found that the `diag` operator does not support N-d arrays where `N > 2`. According to my own experience, it could be made more useful if the `N > 2` cases are properly designed. For example, I find it troublesome to take the diagonals of several matrices of the same shape at the same time. I know this task could be accomplished with a combination of `arange`, `tile` and `pick`, but it would be very complicated, confusing and error-prone. To support this, the behaviour when `N > 2` could be designed as taking the diagonal of the last two axes, i.e., when fed with an array of shape `[d1, d2, d3, ..., dn-2, dn-1, dn]`, where the diagonal of `[dn-1, dn]` is of length `k`, `diag` would return an array of shape `[d1, d2, d3, ..., dn-2, k]`. Of course, this could be designed to be more flexible (allowing specifying the axes to reduce, for example).
   
   PyTorch provides a `diag` operator that behaves in the same way. Tensorflow actually splits it into two operators, `diag` and `diag_part`, the former of which constructs diagonal matrices and the latter takes diagonals from matrices. They are designed to support `N > 2` but not in a way I find useful or flexible.
   
   On the MXNet forum: https://discuss.mxnet.io/t/diag-for-n-d-arrays/1707

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