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# tf.sparse.softmax

Applies softmax to a batched N-D `SparseTensor`.

The inputs represent an N-D SparseTensor with logical shape `[..., B, C]` (where `N >= 2`), and with indices sorted in the canonical lexicographic order.

This op is equivalent to applying the normal `tf.nn.softmax()` to each innermost logical submatrix with shape `[B, C]`, but with the catch that the implicitly zero elements do not participate. Specifically, the algorithm is equivalent to:

(1) Applies `tf.nn.softmax()` to a densified view of each innermost submatrix with shape `[B, C]`, along the size-C dimension; (2) Masks out the original implicitly-zero locations; (3) Renormalizes the remaining elements.

Hence, the `SparseTensor` result has exactly the same non-zero indices and shape.

#### Example:

``````# First batch:
# [?   e.]
# [1.  ? ]
# Second batch:
# [e   ? ]
# [e   e ]
shape = [2, 2, 2]  # 3-D SparseTensor
values = np.asarray([[[0., np.e], [1., 0.]], [[np.e, 0.], [np.e, np.e]]])
indices = np.vstack(np.where(values)).astype(np.int64).T

result = tf.sparse.softmax(tf.sparse.SparseTensor(indices, values, shape))
# ...returning a 3-D SparseTensor, equivalent to:
# [?   1.]     [1    ?]
# [1.  ? ] and [.5  .5]
# where ? means implicitly zero.
``````

`sp_input` N-D `SparseTensor`, where `N >= 2`.
`name` optional name of the operation.

`output` N-D `SparseTensor` representing the results.