|TensorFlow 1 version||View source on GitHub|
Parallel map on the list of tensors unpacked from
elems on dimension 0.
Compat aliases for migration
See Migration guide for more details.
tf.vectorized_map( fn, elems, fallback_to_while_loop=True )
Used in the notebooks
|Used in the guide|
This method works similar to
tf.map_fn but is optimized to run much faster,
possibly with a much larger memory footprint. The speedups are obtained by
vectorization (see Auto-Vectorizing TensorFlow Graphs: Jacobians,
Auto-Batching and Beyond). The idea
behind vectorization is to semantically launch all the invocations of
parallel and fuse corresponding operations across all these invocations. This
fusion is done statically at graph generation time and the generated code is
often similar in performance to a manually fused version.
tf.vectorized_map fully parallelizes the batch, this method will
generally be significantly faster than using
tf.map_fn, especially in eager
mode. However this is an experimental feature and currently has a lot of
- There should be no data dependency between the different semantic
fn, i.e. it should be safe to map the elements of the inputs in any order.
- Stateful kernels may mostly not be supported since these often imply a data dependency. We do support a limited set of such stateful kernels though (like RandomFoo, Variable operations like reads, etc).
fnhas limited support for control flow operations.
fnshould return nested structure of Tensors or Operations. However if an Operation is returned, it should have zero outputs.
- The shape and dtype of any intermediate or output tensors in the
fnshould not depend on the input to
def outer_product(a): return tf.tensordot(a, a, 0) batch_size = 100 a = tf.ones((batch_size, 32, 32)) c = tf.vectorized_map(outer_product, a) assert c.shape == (batch_size, 32, 32, 32, 32)
# Computing per-example gradients batch_size = 10 num_features = 32 layer = tf.keras.layers.Dense(1) def model_fn(arg): with tf.GradientTape() as g: inp, label = arg inp = tf.expand_dims(inp, 0) label = tf.expand_dims(label, 0) prediction = layer(inp) loss = tf.nn.l2_loss(label - prediction) return g.gradient(loss, (layer.kernel, layer.bias)) inputs = tf.random.uniform([batch_size, num_features]) labels = tf.random.uniform([batch_size, 1]) per_example_gradients = tf.vectorized_map(model_fn, (inputs, labels)) assert per_example_gradients.shape == (batch_size, num_features, 1) assert per_example_gradients.shape == (batch_size, 1)
The callable to be performed. It accepts one argument, which will have
the same (possibly nested) structure as
A tensor or (possibly nested) sequence of tensors, each of which will
be unpacked along their first dimension. The nested sequence of the
resulting slices will be mapped over by
If true, on failing to vectorize an operation,
the unsupported op is wrapped in a tf.while_loop to execute the map
iterations. Note that this fallback only happens for unsupported ops and
other parts of
A tensor or (possibly nested) sequence of tensors. Each tensor packs the
results of applying fn to tensors unpacked from elems along the first
dimension, from first to last.
Although they are less common as user-visible inputs and outputs, note that
tensors of type
||If vectorization fails and fallback_to_while_loop is False.|