Class: TensorStream::MathGradients

Inherits:
Object
  • Object
show all
Extended by:
OpHelper
Defined in:
lib/tensor_stream/math_gradients.rb

Overview

Class that provides auto-differentiation

Class Method Summary collapse

Methods included from OpHelper

_op, cons, dtype_eval, format_source, fp_type?, i_cons, i_op, shape_eval, val_to_dtype

Class Method Details

._broadcast_gradient_args(input_a, input_b) ⇒ Object 



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# File 'lib/tensor_stream/math_gradients.rb', line 200

def self._broadcast_gradient_args(input_a, input_b)
  [_op(:broadcast_gradient_args, input_b, input_a), _op(:broadcast_gradient_args, input_a, input_b)]
end

._broadcast_transform(input_a, input_b) ⇒ Object 



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# File 'lib/tensor_stream/math_gradients.rb', line 204

def self._broadcast_transform(input_a, input_b)
  _op(:broadcast_transform, input_a, input_b)
end

._compute_derivative(node, grad) ⇒ Object 



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# File 'lib/tensor_stream/math_gradients.rb', line 53

def self._compute_derivative(node, grad)
  node.graph.name_scope("#{node.name}_grad") do
    x = node.items[0] if node.items[0]
    y = node.items[1] if node.items[1]

    case node.operation
    when :add
      return [grad, grad] if _shapes_fully_specified_and_equal(x, y)

      sx = tf.shape(x, name: 'add/shape_x')
      sy = tf.shape(y, name: 'add/shape_y')
      rx, ry = _broadcast_gradient_args(sx, sy)
      keep_dims_x = tf.rank(x) == tf.rank(grad)
      keep_dims_y = tf.rank(y) == tf.rank(grad)

      [tf.reduce_sum(grad, rx, name: 'add/reduce_sum_x', keepdims: keep_dims_x),
      tf.reduce_sum(grad, ry, name: 'add/reduce_sum_y', keepdims: keep_dims_y)]
    when :sub
      return [grad, -grad] if _shapes_fully_specified_and_equal(x, y)

      sx = tf.shape(x, name: 'sub/shape_x')
      sy = tf.shape(y, name: 'sub/shape_y')
      rx, ry = _broadcast_gradient_args(sx, sy)
      [tf.reduce_sum(grad, rx), -tf.reduce_sum(grad, ry)]
    when :mul
      sx = tf.shape(x)
      sy = tf.shape(y)
      rx, ry = _broadcast_gradient_args(sx, sy)

      [ tf.reduce_sum(tf.mul(grad, y), rx),
        tf.reduce_sum(tf.mul(x, grad), ry)]
    when :div
      sx = i_op(:shape, x)
      sy = i_op(:shape, y)
      rx, ry = _broadcast_gradient_args(sx, sy)

      [tf.reduce_sum(tf.div(grad, y), rx),
      tf.reduce_sum(grad * tf.div(tf.div(-x, y), y),
                              ry)]
    when :matmul
      t_a = node.options[:transpose_a]
      t_b = node.options[:transpose_b]

      s0 =  tf.shape(x)
      s1 =  tf.shape(y)

      identity_0 = tf.ones([ s0[0], s1[1] ], dtype: x.data_type, name: 'matmul/identity0')
      identity_1 = tf.ones([ s0[0], s1[1] ], dtype: y.data_type, name: 'matmul/identity1')

      grad_a, grad_b = nil
      if !t_a && !t_b
        grad_a = tf.matmul(identity_0, y, transpose_b: true)
        grad_b = tf.matmul(x, identity_1, transpose_a: true)
      elsif !ta && tb
        grad_a = tf.matmul(identity_0, y)
        grad_b = tf.matmul(identity_1, x, transpose_a: true)
      elsif t_a && !t_b
        grad_a = tf.matmul(y, identity_0, transpose_b: true)
        grad_b = tf.matmul(x, identity_1)
      elsif t_a && t_b
        grad_a = tf.matmul(y, identity_0, transpose_a: true, transpose_b: true)
        grad_b = tf.matmul(identity_1, x, transpose_a: true, transpose_b: true)
      end

      grad_a = i_op(:mul, grad, grad_a, name: 'matmul/grad_a_norm_mul_da')
      grad_b = i_op(:mul, grad, grad_b, name: 'matmul/grad_b_norm_mul_db')

      [grad_a, grad_b]
    when :sin
      grad * tf.cos(x)
    when :tanh
      grad * i_op(:tanh_grad, x)
    when :pow
      z = node
      sx = tf.shape(x)
      sy = tf.shape(y)
      rx, ry = _broadcast_gradient_args(sx, sy)
      gx = tf.reshape(
        tf.reduce_sum(grad * y * tf.pow(x, y - 1), rx), sx)

      log_x = tf.where(x > 0, tf.log(x), tf.zeros_like(x))
      gy = tf.reshape(tf.reduce_sum(grad * z * log_x, ry), sy)

      [gx, gy]
    when :abs
      grad * tf.sign(x)
    when :log
      grad * tf.reciprocal(x)
    when :tanh
      i_op(:tanh_grad, x) * grad
    when :cos
      -grad * tf.sin(x)
    when :max
      x_mask = tf.where(x > y, tf.ones_like(x), tf.zeros_like(y))
      y_mask = tf.where(x < y, tf.zeros_like(x), tf.ones_like(y))
      [x_mask * grad, y_mask * grad]
    when :tan
      secx = tf.reciprocal(tf.cos(x))
      secx2 = tf.square(secx)
      grad * secx2
    when :negate
      -grad
    when :exp
      grad * node
    when :identity
      grad
    when :sum
      _sum_grad(x, y, grad)
    when :reciprocal
      -grad * (tf.constant(1, dtype: x.dtype) / x**2)
    when :sqrt
      tf.constant(1, dtype: x.dtype) / (tf.constant(2, dtype: x.dtype) * tf.sqrt(x)) * grad
    when :stop_gradient
      tf.zeros_like(grad)
    when :square
      y = tf.constant(2.0, dtype: x.dtype)
      tf.multiply(grad, tf.multiply(x, y))
    when :where
      x_mask = i_op(:where, i_op(:ones_like, x), i_op(:zeros_like, y), pred: node.options[:pred])
      y_mask = i_op(:where, i_op(:zeros_like, x), i_op(:ones_like, y), pred: node.options[:pred])
      [x_mask * grad, y_mask * grad]
    when :cond
      x_cond = i_op(:cond, i_op(:ones_like, x), i_op(:zeros_like, y), pred: node.options[:pred])
      y_cond = i_op(:cond, i_op(:zeros_like, x), i_op(:ones_like, x), pred: node.options[:pred])
      [x_cond * grad, y_cond * grad]
    when :mean
      sum_grad = _sum_grad(x, y, grad)
      input_shape = tf.shape(x)
      output_shape = tf.shape(node)
      factor = _safe_shape_div(tf.reduce_prod(input_shape), tf.reduce_prod(output_shape))
      tf.div(sum_grad, tf.cast(factor, sum_grad.data_type))
    when :log1p
      grad * tf.reciprocal(i_cons(1, data_type: grad.data_type) + x)
    when :sigmoid
      i_op(:sigmoid_grad, x, grad)
    when :zeros_like
      # non differentiable
      nil
    when :argmin, :argmax
      # non differentiable
      [nil, nil]
    else
      raise "no derivative op for #{node.operation}"
    end
  end
end

._include?(arr, obj) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/tensor_stream/math_gradients.rb', line 228

def self._include?(arr, obj)
  arr.each { |a| return true if a.equal?(obj) }
  false
end

._min_or_max_grad(op, grad) ⇒ Object 



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# File 'lib/tensor_stream/math_gradients.rb', line 221

def self._min_or_max_grad(op, grad)
  y = op
  indicators = tf.cast(tf.equal(y, op.items[0]), grad.data_type)
  num_selected = tf.reduce_sum(indicators, op.items[1])
  _safe_shape_div(indicators, num_selected) * grad
end

._op_supports_broadcast?(node) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/tensor_stream/math_gradients.rb', line 216

def self._op_supports_broadcast?(node)
  return true if i[add sub div mul pow].include?(node.operation)
  false
end

._propagate(grad, tensor, stop_tensor, nodes_to_compute, stop_gradients = []) ⇒ Object 



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# File 'lib/tensor_stream/math_gradients.rb', line 25

def self._propagate(grad, tensor, stop_tensor, nodes_to_compute, stop_gradients = [])
  return grad * i_op(:ones_like, stop_tensor) if stop_tensor.equal?(tensor)
  return i_op(:zeros_like, stop_tensor) if stop_gradients && _include?(stop_gradients, tensor)
  return i_op(:zeros_like, stop_tensor) unless tensor.is_a?(Operation)

  computed_op = if _op_supports_broadcast?(tensor)
                  _compute_derivative(tensor, _broadcast_transform(tensor, grad)[1])
                else
                  _compute_derivative(tensor, grad)
                end

  if computed_op.is_a?(Array)
    partials = []
    computed_op.each_with_index do |op_grad, index|
      next if op_grad.nil?

      if nodes_to_compute.include?(tensor.items[index].name)
        partials << _propagate(op_grad, tensor.items[index], stop_tensor, nodes_to_compute, stop_gradients)
      end
    end

    partials.reduce(:+)
  else
    return tf.zeros_like(stop_tensor) if computed_op.nil?
    _propagate(computed_op, tensor.items[0], stop_tensor, nodes_to_compute, stop_gradients)
  end
end

._safe_shape_div(x, y) ⇒ Object 



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# File 'lib/tensor_stream/math_gradients.rb', line 208

def self._safe_shape_div(x, y)
  x / tf.maximum(y, 1)
end

._shape_full_specified(tensor) ⇒ Object 



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# File 'lib/tensor_stream/math_gradients.rb', line 240

def self._shape_full_specified(tensor)
  return false if tensor.shape.nil?
  return false if tensor.shape.shape.nil?

  tensor.shape.shape.each { |s| return false if s.nil? }
  true
end

._shapes_fully_specified_and_equal(x, y) ⇒ Object 



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# File 'lib/tensor_stream/math_gradients.rb', line 233

def self._shapes_fully_specified_and_equal(x, y)
 return false if !_shape_full_specified(x) || !_shape_full_specified(y)
 return false if x.shape.shape != y.shape.shape
 
 true
end

._sum_grad(x, y, grad) ⇒ Object 



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# File 'lib/tensor_stream/math_gradients.rb', line 212

def self._sum_grad(x, y, grad)
  tf.ones_like(x) * grad
end

.derivative(tensor, wrt_dx, options = {}) ⇒ Object 



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# File 'lib/tensor_stream/math_gradients.rb', line 10

def self.derivative(tensor, wrt_dx, options = {})
  return i_op(:ones_like, tensor) if tensor.equal?(wrt_dx)
  return i_op(:zeros_like, tensor) unless wrt_dx.consumers.include?(tensor.name)

  nodes_to_compute = wrt_dx.consumers.select do |t|
    node = tensor.graph.nodes[t]
    node.consumers.include?(tensor.name) || node.equal?(tensor)
  end.compact + [wrt_dx.name]

  grad = i_op(:ones_like, wrt_dx)

  result = _propagate(grad, tensor, wrt_dx, nodes_to_compute, options[:stop_gradients] || [])
  i_op(:truncate, result, tf.shape(wrt_dx))
end

.tf ⇒ Object 



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# File 'lib/tensor_stream/math_gradients.rb', line 6

def self.tf
  TensorStream
end