相当于合并了softmax和cross_entropy两步
sparse_softmax_cross_entropy_with_logits(_sentinel=None, labels=None, logits=None, name=None)
Computes sparse softmax cross entropy between `logits` and `labels`.
Measures the probability error in discrete classification tasks in which the
classes are mutually exclusive (each entry is in exactly one class). For
example, each CIFAR-10 image is labeled with one and only one label: an image
can be a dog or a truck, but not both.
**NOTE:** For this operation, the probability of a given label is considered
exclusive. That is, soft classes are not allowed, and the `labels` vector
must provide a single specific index for the true class for each row of
`logits` (each minibatch entry). For soft softmax classification with
a probability distribution for each entry, see
`softmax_cross_entropy_with_logits`.
**WARNING:** This op expects unscaled logits, since it performs a `softmax`
on `logits` internally for efficiency. Do not call this op with the
output of `softmax`, as it will produce incorrect results.
A common use case is to have logits of shape `[batch_size, num_classes]` and
labels of shape `[batch_size]`. But higher dimensions are supported.
**Note that to avoid confusion, it is required to pass only named arguments to
this function.**
Args:
_sentinel: Used to prevent positional parameters. Internal, do not use.
labels: `Tensor` of shape `[d_0, d_1, ..., d_{r-1}]` (where `r` is rank of
`labels` and result) and dtype `int32` or `int64`. Each entry in `labels`
must be an index in `[0, num_classes)`. Other values will raise an
exception when this op is run on CPU, and return `NaN` for corresponding
loss and gradient rows on GPU.
logits: Unscaled log probabilities of shape
`[d_0, d_1, ..., d_{r-1}, num_classes]` and dtype `float32` or `float64`.
name: A name for the operation (optional).
Returns:
A `Tensor` of the same shape as `labels` and of the same type as `logits`
with the softmax cross entropy loss.
Raises:
ValueError: If logits are scalars (need to have rank >= 1) or if the rank
of the labels is not equal to the rank of the logits minus one.
