Python tensorflow.GradientTape() Examples

def train_step(self, features, labels):
        """
        Train step.

        Args:
            features: Input features.
            labels: The labels.

        Returns:
            Loss value.

        """
        with tf.GradientTape() as tape:
            loss = self._loss(
                self._context, features=features, labels=labels, training=True
            )

        gradients = tape.gradient(loss, self._model.trainable_variables)
        self._optimizer.apply_gradients(zip(gradients, self._model.trainable_variables))
        return loss 

def wrapped_tf_function(points, label):
  """Performs one step of minimization of the loss."""
  # --- subsampling (order DO matter)
  points = points[0:FLAGS.num_points, ...]

  # --- augmentation
  if FLAGS.augment:
    points = tf.map_fn(augment.rotate, points)
    points = augment.jitter(points)

  # --- training
  with tf.GradientTape() as tape:
    logits = model(points, training=True)
    loss = model.loss(label, logits)
  variables = model.trainable_variables
  gradients = tape.gradient(loss, variables)
  optimizer.apply_gradients(zip(gradients, variables))
  return loss 

def train_step(self, inputs):
    """One train step.
    Args:
      inputs: one batch input.
    Returns:
      loss: Scaled loss.
    """

    image, label = inputs
    with tf.GradientTape() as tape:
      predictions = self.model(image, training=True)

      loss = self.compute_loss(predictions,label,training=True)

    gradients = tape.gradient(loss, self.model.trainable_variables)
    gradients = [(tf.clip_by_value(grad, -5.0, 5.0))
                 for grad in gradients]
    self.optimizer.apply_gradients(zip(gradients,
                                       self.model.trainable_variables))

    return loss 

def train_step(self, inp, tar):
        tar_inp = tar[:, :-1]
        tar_real = tar[:, 1:]

        enc_padding_mask, combined_mask, dec_padding_mask = self.mask_encoder.create_masks(inp, tar_inp)

        with tf.GradientTape() as tape:
            predictions, _ = self.transformer(inp, tar_inp,
                                              True,
                                              enc_padding_mask,
                                              combined_mask,
                                              dec_padding_mask)
            loss = self.loss_function(tar_real, predictions)

        gradients = tape.gradient(loss, self.transformer.trainable_variables)
        self.optimizer.apply_gradients(zip(gradients, self.transformer.trainable_variables))

        self.train_loss(loss)
        self.train_accuracy(tar_real, predictions) 

def _train_body(self, agent_states, agent_next_states, expert_states, expert_next_states):
        epsilon = 1e-8
        with tf.device(self.device):
            with tf.GradientTape() as tape:
                real_logits = self.disc([expert_states, expert_next_states])
                fake_logits = self.disc([agent_states, agent_next_states])
                loss = -(tf.reduce_mean(tf.math.log(real_logits + epsilon)) +
                         tf.reduce_mean(tf.math.log(1. - fake_logits + epsilon)))
            grads = tape.gradient(loss, self.disc.trainable_variables)
            self.optimizer.apply_gradients(
                zip(grads, self.disc.trainable_variables))

        accuracy = \
            tf.reduce_mean(tf.cast(real_logits >= 0.5, tf.float32)) / 2. + \
            tf.reduce_mean(tf.cast(fake_logits < 0.5, tf.float32)) / 2.
        js_divergence = self._compute_js_divergence(
            fake_logits, real_logits)
        return loss, accuracy, js_divergence 

def _train_body(self, states, actions, next_states, rewards, done, weights):
        with tf.device(self.device):
            with tf.GradientTape() as tape:
                if self._enable_categorical_dqn:
                    td_errors = self._compute_td_error_body_distributional(
                        states, actions, next_states, rewards, done)
                    q_func_loss = tf.reduce_mean(
                        huber_loss(tf.negative(td_errors),
                                   delta=self.max_grad) * weights)
                else:
                    td_errors = self._compute_td_error_body(
                        states, actions, next_states, rewards, done)
                    q_func_loss = tf.reduce_mean(
                        huber_loss(td_errors,
                                   delta=self.max_grad) * weights)

            q_func_grad = tape.gradient(
                q_func_loss, self.q_func.trainable_variables)
            self.q_func_optimizer.apply_gradients(
                zip(q_func_grad, self.q_func.trainable_variables))

            return td_errors, q_func_loss 

def verify_funcs_are_equivalent(dtype):
    x_np = np.random.uniform(-10, 10, size=(4, 4)).astype(dtype)
    x = tf.convert_to_tensor(x_np)
    lower = np.random.uniform(-10, 10)
    upper = lower + np.random.uniform(0, 10)

    with tf.GradientTape(persistent=True) as t:
        t.watch(x)
        y_native = _hardshrink_custom_op(x, lower, upper)
        y_py = _hardshrink_py(x, lower, upper)

    test_utils.assert_allclose_according_to_type(y_native, y_py)

    grad_native = t.gradient(y_native, x)
    grad_py = t.gradient(y_py, x)

    test_utils.assert_allclose_according_to_type(grad_native, grad_py) 

def _train_body(self, agent_states, agent_acts, expert_states, expert_acts):
        epsilon = 1e-8
        with tf.device(self.device):
            with tf.GradientTape() as tape:
                real_logits = self.disc([expert_states, expert_acts])
                fake_logits = self.disc([agent_states, agent_acts])
                loss = -(tf.reduce_mean(tf.math.log(real_logits + epsilon)) +
                         tf.reduce_mean(tf.math.log(1. - fake_logits + epsilon)))
            grads = tape.gradient(loss, self.disc.trainable_variables)
            self.optimizer.apply_gradients(
                zip(grads, self.disc.trainable_variables))

        accuracy = \
            tf.reduce_mean(tf.cast(real_logits >= 0.5, tf.float32)) / 2. + \
            tf.reduce_mean(tf.cast(fake_logits < 0.5, tf.float32)) / 2.
        js_divergence = self._compute_js_divergence(
            fake_logits, real_logits)
        return loss, accuracy, js_divergence 

def verify_funcs_are_equivalent(dtype):
    x_np = np.random.uniform(-10, 10, size=(4, 4)).astype(dtype)
    x = tf.convert_to_tensor(x_np)
    lower = np.random.uniform(-10, 10)
    upper = lower + np.random.uniform(0, 10)

    with tf.GradientTape(persistent=True) as t:
        t.watch(x)
        y_native = softshrink(x, lower, upper)
        y_py = _softshrink_py(x, lower, upper)

    test_utils.assert_allclose_according_to_type(y_native, y_py)

    grad_native = t.gradient(y_native, x)
    grad_py = t.gradient(y_py, x)

    test_utils.assert_allclose_according_to_type(grad_native, grad_py) 

def test_interpolation_gradient():
    """Correctness of gradients is assumed. We compute them
    and check they exist.
    """
    tp = _QuadraticPlusSinProblemND()
    (query_points, _, train_points, train_values) = tp.get_problem(optimizable=True)

    regularization = 0.001
    for interpolation_order in (1, 2, 3, 4):

        with tf.GradientTape() as g:
            interpolator = interpolate_spline(
                train_points,
                train_values,
                query_points,
                interpolation_order,
                regularization,
            )

        gradients = g.gradient(interpolator, train_points).numpy()
        assert np.sum(np.abs(gradients)) != 0 

def test_gradients_exist():
    """Check that backprop can run.

    The correctness of the gradients is assumed, since the forward
    propagation is tested to be correct and we only use built-in tf
    ops. However, we perform a simple test to make sure that
    backprop can actually run.
    """
    batch_size, height, width, num_channels = [4, 5, 6, 7]
    image_shape = [batch_size, height, width, num_channels]
    image = tf.random.normal(image_shape)
    flow_shape = [batch_size, height, width, 2]
    flows = tf.Variable(tf.random.normal(shape=flow_shape) * 0.25, dtype=tf.float32)

    with tf.GradientTape() as t:
        interp = dense_image_warp(image, flows)

    grads = t.gradient(interp, flows).numpy()
    assert np.sum(np.abs(grads)) != 0 

def _create_gradient_fn(self, variables):
    """Create a function that computes gradients and applies them to the model.
    Because of the way TensorFlow function tracing works, we need to create a
    separate function for each new set of variables.
    """

    @tf.function(experimental_relax_shapes=True)
    def apply_gradient_for_batch(inputs, labels, weights, loss):
      with tf.GradientTape() as tape:
        outputs = self.model(inputs, training=True)
        if isinstance(outputs, tf.Tensor):
          outputs = [outputs]
        if self._loss_outputs is not None:
          outputs = [outputs[i] for i in self._loss_outputs]
        batch_loss = loss(outputs, labels, weights)
      if variables is None:
        vars = self.model.trainable_variables
      else:
        vars = variables
      grads = tape.gradient(batch_loss, vars)
      self._tf_optimizer.apply_gradients(zip(grads, vars))
      self._global_step.assign_add(1)
      return batch_loss

    return apply_gradient_for_batch 

def call(self, inputs, conditional_inputs):
    with tf.GradientTape() as tape:
      for layer in inputs:
        tape.watch(layer)
      output = self.discriminator(_list_or_tensor(inputs + conditional_inputs))
    gradients = tape.gradient(output, inputs)
    gradients = [g for g in gradients if g is not None]
    if len(gradients) > 0:
      norm2 = 0.0
      for g in gradients:
        g2 = tf.square(g)
        dims = len(g.shape)
        if dims > 1:
          g2 = tf.reduce_sum(g2, axis=list(range(1, dims)))
        norm2 += g2
      penalty = tf.square(tf.sqrt(norm2) - 1.0)
      penalty = self.gan.gradient_penalty * tf.reduce_mean(penalty)
    else:
      penalty = 0.0
    return [output, penalty] 

def train_on_current_task(self, optimization_steps=1, restore=True):
    """Perform a few steps of gradient descent to fine tune the model on the current task.

    Parameters
    ----------
    optimization_steps: int
      the number of steps of gradient descent to perform
    restore: bool
      if True, restore the model from the most recent checkpoint before optimizing
    """
    if restore:
      self.restore()
    variables = self.learner.variables
    for i in range(optimization_steps):
      inputs = self.learner.get_batch()
      with tf.GradientTape() as tape:
        loss, _ = self.learner.compute_model(inputs, variables, True)
      gradients = tape.gradient(loss, variables)
      self._tf_task_optimizer.apply_gradients(zip(gradients, variables)) 

def _compute_meta_loss(self, inputs, inputs2, variables):
    """This is called during fitting to compute the meta-loss (the loss after a
    few steps of optimization), and its gradient.
    """
    updated_variables = variables
    with tf.GradientTape() as meta_tape:
      for k in range(self.optimization_steps):
        with tf.GradientTape() as tape:
          loss, _ = self.learner.compute_model(inputs, updated_variables, True)
        gradients = tape.gradient(loss, updated_variables)
        updated_variables = [
            v if g is None else v - self.learning_rate * g
            for v, g in zip(updated_variables, gradients)
        ]
      meta_loss, _ = self.learner.compute_model(inputs2, updated_variables,
                                                True)
    meta_gradients = meta_tape.gradient(meta_loss, variables)
    return meta_loss, meta_gradients 

def test_swish_grad(self):
        def swish_grad(x, beta):
            return (
                beta * (2 - beta * x * np.tanh(beta * x / 2)) / (1 + np.cosh(beta * x))
            )

        x = testing_utils.generate_real_values_with_zeros(shape=(8, 3, 3, 16))
        tf_x = tf.Variable(x)
        with tf.GradientTape() as tape:
            activation = lq.quantizers.SwishSign()(tf_x)
        grad = tape.gradient(activation, tf_x)
        np.testing.assert_allclose(grad.numpy(), swish_grad(x, beta=5.0))

        with tf.GradientTape() as tape:
            activation = lq.quantizers.SwishSign(beta=10.0)(tf_x)
        grad = tape.gradient(activation, tf_x)
        np.testing.assert_allclose(grad.numpy(), swish_grad(x, beta=10.0)) 

def pretrain_step(model, x, y):
    """
    Single step of generator pre-training.
    Args:
        model: A model object with a tf keras compiled generator.
        x: The low resolution image tensor.
        y: The high resolution image tensor.
    """
    with tf.GradientTape() as tape:
        fake_hr = model.generator(x)
        loss_mse = tf.keras.losses.MeanSquaredError()(y, fake_hr)

    grads = tape.gradient(loss_mse, model.generator.trainable_variables)
    model.gen_optimizer.apply_gradients(zip(grads, model.generator.trainable_variables))

    return loss_mse 

def test_that_backprop_runs():
    """Making sure the gradients can be computed."""
    batch_size = 1
    image_height = 9
    image_width = 12
    image = tf.Variable(
        np.random.uniform(size=[batch_size, image_height, image_width, 3]),
        dtype=tf.float32,
    )
    control_point_locations = [[3.0, 3.0]]
    control_point_locations = tf.constant(
        np.float32(np.expand_dims(control_point_locations, 0))
    )
    control_point_displacements = [[0.25, -0.5]]
    control_point_displacements = tf.constant(
        np.float32(np.expand_dims(control_point_displacements, 0))
    )

    with tf.GradientTape() as t:
        warped_image, _ = sparse_image_warp(
            image,
            control_point_locations,
            control_point_locations + control_point_displacements,
            num_boundary_points=3,
        )

    gradients = t.gradient(warped_image, image).numpy()
    assert np.sum(np.abs(gradients)) != 0 

def minimize(self, loss, var_list, grad_loss=None, name=None, decay_var_list=None):
        """Minimize `loss` by updating `var_list`.

        This method simply computes gradient using `tf.GradientTape` and calls
        `apply_gradients()`. If you want to process the gradient before
        applying then call `tf.GradientTape` and `apply_gradients()` explicitly
        instead of using this function.

        Args:
            loss: A callable taking no arguments which returns the value to
                minimize.
            var_list: list or tuple of `Variable` objects to update to
                minimize `loss`, or a callable returning the list or tuple of
                `Variable` objects. Use callable when the variable list would
                otherwise be incomplete before `minimize` since the variables
                are created at the first time `loss` is called.
            grad_loss: Optional. A `Tensor` holding the gradient computed for
                `loss`.
            decay_var_list: Optional list of variables to be decayed. Defaults
                to all variables in var_list.
            name: Optional name for the returned operation.
        Returns:
            An Operation that updates the variables in `var_list`.
        Raises:
            ValueError: If some of the variables are not `Variable` objects.
        """
        self._decay_var_list = (
            set([_ref(v) for v in decay_var_list]) if decay_var_list else False
        )
        return super().minimize(loss, var_list=var_list, grad_loss=grad_loss, name=name) 

def test_identity_ste_grad(self, fn):
        x = testing_utils.generate_real_values_with_zeros(shape=(8, 3, 3, 16))
        tf_x = tf.Variable(x)
        with tf.GradientTape() as tape:
            activation = fn(tf_x)
        grad = tape.gradient(activation, tf_x)
        np.testing.assert_allclose(grad.numpy(), np.ones_like(x)) 

def _values_and_jacobian(residuals, variables):
  """Computes the residual values and the Jacobian matrix.

  Args:
    residuals: A list of residuals.
    variables: A list of variables.

  Returns:
    The residual values and the Jacobian matrix.
  """

  def _compute_residual_values(residuals, variables):
    """Computes the residual values."""
    return tf.concat([
        tf.reshape(residual(*variables), shape=(-1,)) for residual in residuals
    ],
                     axis=-1)

  def _compute_jacobian(values, variables, tape):
    """Computes the Jacobian matrix."""
    jacobians = tape.jacobian(
        values, variables, unconnected_gradients=tf.UnconnectedGradients.ZERO)
    return tf.concat([
        tf.reshape(jacobian, shape=(tf.shape(input=jacobian)[0], -1))
        for jacobian in jacobians
    ],
                     axis=-1)

  with tf.GradientTape(watch_accessed_variables=False, persistent=True) as tape:
    for variable in variables:
      tape.watch(variable)
    values = _compute_residual_values(residuals, variables)
  jacobian = _compute_jacobian(values, variables, tape)
  del tape
  values = tf.expand_dims(values, axis=-1)
  return values, jacobian 

def train_one_step(model, optimizer, idx, value, label):
    with tf.GradientTape() as tape:
        output = model(idx, value)
        loss = cross_entropy_loss(y_true=label, y_pred=output)

        reg_loss = []
        for p in model.trainable_variables:
            reg_loss.append(tf.nn.l2_loss(p))
        reg_loss = tf.reduce_sum(tf.stack(reg_loss))
        loss = loss + model.reg_l2 * reg_loss

    grads = tape.gradient(loss, model.trainable_variables)
    grads = [tf.clip_by_norm(g, 100) for g in grads]
    optimizer.apply_gradients(grads_and_vars=zip(grads, model.trainable_variables))
    return loss 

def testSparseGaussianProcess(self):
    dataset_size = 10
    batch_size = 3
    input_dim = 4
    output_dim = 5
    features = tf.to_float(np.random.rand(batch_size, input_dim))
    labels = tf.to_float(np.random.rand(batch_size, output_dim))
    model = gaussian_process.SparseGaussianProcess(output_dim, num_inducing=2)
    with tf.GradientTape() as tape:
      predictions = model(features)
      nll = -tf.reduce_mean(predictions.distribution.log_prob(labels))
      kl = sum(model.losses) / dataset_size
      loss = nll + kl

    self.evaluate(tf.global_variables_initializer())
    grads = tape.gradient(nll, model.variables)
    for grad in grads:
      self.assertIsNotNone(grad)

    loss_val, predictions_val = self.evaluate([loss, predictions])
    self.assertEqual(loss_val.shape, ())
    self.assertGreaterEqual(loss_val, 0.)
    self.assertEqual(predictions_val.shape, (batch_size, output_dim)) 

def _train_step(self,text,labels):
        with tf.GradientTape() as tape:
            predictions = self.model(text,training=True)
            loss = self.loss_object(labels,predictions)
        gradients = tape.gradient(loss,self.model.trainable_variables)
        self.optimizer.apply_gradients(zip(gradients,self.model.trainable_variables))
        return predictions, loss 

def backward_grads_and_vars(self, y, dy, training=True):
        """Manually compute backward gradients given input and output grads."""
        dy1, dy2 = tf.split(dy, num_or_size_splits=2, axis=self.axis)

        with tf.GradientTape(persistent=True) as tape:
            y = tf.identity(y)
            tape.watch(y)
            y1, y2 = tf.split(y, num_or_size_splits=2, axis=self.axis)
            z1 = y1
            gz1 = self.g(z1, training=training)
            x2 = y2 - gz1
            fx2 = self.f(x2, training=training)
            x1 = z1 - fx2

            grads_combined = tape.gradient(
                gz1, [z1] + self.g.trainable_variables, output_gradients=dy2)
            dz1 = dy1 + grads_combined[0]
            dg = grads_combined[1:]
            dx1 = dz1

            grads_combined = tape.gradient(
                fx2, [x2] + self.f.trainable_variables, output_gradients=dz1)
            dx2 = dy2 + grads_combined[0]
            df = grads_combined[1:]

            del tape

        grads = df + dg
        vars_ = self.f.trainable_variables + self.g.trainable_variables

        x = tf.concat([x1, x2], axis=self.axis)
        dx = tf.concat([dx1, dx2], axis=self.axis)

        return x, dx, grads, vars_ 

def test_ste_grad(self, fn):
        @np.vectorize
        def ste_grad(x):
            if np.abs(x) <= 1:
                return 1.0
            return 0.0

        x = testing_utils.generate_real_values_with_zeros(shape=(8, 3, 3, 16))
        tf_x = tf.Variable(x)
        with tf.GradientTape() as tape:
            activation = fn(tf_x)
        grad = tape.gradient(activation, tf_x)
        np.testing.assert_allclose(grad.numpy(), ste_grad(x))

    # Test with and without default threshold 

def test_approx_sign_grad(self):
        @np.vectorize
        def approx_sign_grad(x):
            if np.abs(x) <= 1:
                return 2 - 2 * np.abs(x)
            return 0.0

        x = testing_utils.generate_real_values_with_zeros(shape=(8, 3, 3, 16))
        tf_x = tf.Variable(x)
        with tf.GradientTape() as tape:
            activation = lq.quantizers.ApproxSign()(tf_x)
        grad = tape.gradient(activation, tf_x)
        np.testing.assert_allclose(grad.numpy(), approx_sign_grad(x)) 

def backward_grads_and_vars(self, x, y, dy, training=True):
        """Apply reversible block backward to outputs."""

        grads_all = []
        vars_all = []

        for i in reversed(range(len(self.blocks))):
            block = self.blocks[i]
            if i == 0:
                # First block usually contains downsampling that can't be reversed
                with tf.GradientTape() as tape:
                    x = tf.identity(x)
                    tape.watch(x)
                    y = block(x, training=training)

                    grads_combined = tape.gradient(
                        y, [x] + block.trainable_variables, output_gradients=dy)
                    dy = grads_combined[0]
                    grads_all += grads_combined[1:]
                    vars_all += block.trainable_variables
            else:
                y, dy, grads, vars_ = block.backward_grads_and_vars(
                    y, dy, training=training)
                grads_all += grads
                vars_all += vars_

        return dy, grads_all, vars_all 

def backward_grads_and_vars(self, x, y, dy, training=True):
        """Apply reversible block backward to outputs."""

        grads_all = []
        vars_all = []

        for i in reversed(range(len(self.blocks))):
            block = self.blocks[i]
            if i == 0:
                # First block usually contains downsampling that can't be reversed
                with tf.GradientTape() as tape:
                    x = tf.identity(x)
                    tape.watch(x)
                    y = block(x, training=training)

                    grads_combined = tape.gradient(
                        y, [x] + block.trainable_variables, output_gradients=dy)
                    dy = grads_combined[0]
                    grads_all += grads_combined[1:]
                    vars_all += block.trainable_variables
            else:
                y, dy, grads, vars_ = block.backward_grads_and_vars(
                    y, dy, training=training)
                grads_all += grads
                vars_all += vars_

        return dy, grads_all, vars_all 

def test_magnitude_aware_sign_grad(self):
        a = np.random.uniform(-2, 2, (3, 2, 2, 3))
        x = tf.Variable(a)
        with tf.GradientTape() as tape:
            y = lq.quantizers.MagnitudeAwareSign()(x)
        grad = tape.gradient(y, x)

        scale_vector = [
            np.mean(np.reshape(np.abs(a[:, :, :, i]), [-1])) for i in range(3)
        ]

        np.testing.assert_allclose(
            grad.numpy(), np.where(abs(a) < 1, np.ones(a.shape) * scale_vector, 0)
        )