Hi James!
First a comment:



 6fb4b64ff0a68bcbf8fa:

I studied about “Covariance Pooling for Facial Expression Recognition”
this paper offered tensorflow code.
…
every thing changed pytorch.


It sounds like you are trying to translate the “Covariance Pooling”
algorithm from tensorflow to pytorch.  This might well involve
some amount of work, but I would expect it to be doable.
And a question:


I check my gradient eigenvalue,eigenvector(s_f.grad,v_f.grad).
only print none value.
so I consider more backward about symeig.
…
but just problemed om symeig.
any other idea about symeig do not get gradient?


It sounds like you are saying that symeig is giving you “none” for
the value of its gradient.  Is this the issue you are asking about?
(I should note that I haven’t ever used symeig.)
Could you try to isolate this problem and post a small, complete,
runnable pytorch script where you evaluate symeig on some
inputs, call backward(), and then print out the gradients you
get?
If we start with something simple like that, we can try to analyze
your gradient issue.
Best.
K. Frank