Keras-Like API#

1. Introduction#

DLlib provides Keras-like API based on Keras 1.2.2 for distributed deep learning on Apache Spark. Users can easily use the Keras-like API to create a neural network model, and train, evaluate or tune it in a distributed fashion on Spark.

To define a model in Scala using the Keras-like API, one just needs to import the following packages:

import com.intel.analytics.bigdl.dllib.keras.layers._
import com.intel.analytics.bigdl.dllib.keras.models._
import com.intel.analytics.bigdl.dllib.utils.Shape

One of the highlighted features with regard to the new API is shape inference. Users only need to specify the input shape (a Shape object excluding batch dimension, for example, inputShape=Shape(3, 4) for 3D input) for the first layer of a model and for the remaining layers, the input dimension will be automatically inferred.

2. LeNet Example#

Here we use the Keras-like API to define a LeNet CNN model and train it on the MNIST dataset:

import com.intel.analytics.bigdl.numeric.NumericFloat
import com.intel.analytics.bigdl.dllib.keras.layers._
import com.intel.analytics.bigdl.dllib.keras.models._
import com.intel.analytics.bigdl.dllib.utils.Shape

val model = Sequential()
model.add(Reshape(Array(1, 28, 28), inputShape = Shape(28, 28, 1)))
model.add(Convolution2D(6, 5, 5, activation = "tanh").setName("conv1_5x5"))
model.add(MaxPooling2D())
model.add(Convolution2D(12, 5, 5, activation = "tanh").setName("conv2_5x5"))
model.add(MaxPooling2D())
model.add(Flatten())
model.add(Dense(100, activation = "tanh").setName("fc1"))
model.add(Dense(10, activation = "softmax").setName("fc2"))

model.getInputShape().toSingle().toArray // Array(-1, 28, 28, 1)
model.getOutputShape().toSingle().toArray // Array(-1, 10)

3. Shape#

Input and output shapes of a model in the Keras-like API are described by the Shape object in Scala, which can be classified into SingleShape and MultiShape.

SingleShape is just a list of Int indicating shape dimensions while MultiShape is essentially a list of Shape.

Example code to create a shape:

// create a SingleShape
val shape1 = Shape(3, 4)
// create a MultiShape consisting of two SingleShape
val shape2 = Shape(List(Shape(1, 2, 3), Shape(4, 5, 6)))

You can use method toSingle() to cast a Shape to a SingleShape. Similarly, use toMulti() to cast a Shape to a MultiShape.

4. Define a model#

You can define a model either using Sequential API or Functional API. Remember to specify the input shape for the first layer.

After creating a model, you can call the following methods:

getInputShape()

getOutputShape()

  • Return the input or output shape of a model, which is a Shape object. For SingleShape, the first entry is -1 representing the batch dimension. For a model with multiple inputs or outputs, it will return a MultiShape.

setName(name)

  • Set the name of the model.

5. Sequential API#

The model is described as a linear stack of layers in the Sequential API. Layers can be added into the Sequential container one by one and the order of the layers in the model will be the same as the insertion order.

To create a sequential container:

Sequential()

Example code to create a sequential model:

import com.intel.analytics.bigdl.dllib.keras.layers.{Dense, Activation}
import com.intel.analytics.bigdl.dllib.keras.models.Sequential
import com.intel.analytics.bigdl.dllib.utils.Shape

val model = Sequential[Float]()
model.add(Dense[Float](32, inputShape = Shape(128)))
model.add(Activation[Float]("relu"))

6. Functional API#

The model is described as a graph in the Functional API. It is more convenient than the Sequential API when defining some complex model (for example, a model with multiple outputs).

To create an input node:

Input(inputShape = null, name = null)

Parameters:

  • inputShape: A Shape object indicating the shape of the input node, not including batch.

  • name: String to set the name of the input node. If not specified, its name will by default to be a generated string.

To create a graph container:

Model(input, output)

Parameters:

  • input: An input node or an array of input nodes.

  • output: An output node or an array of output nodes.

To merge a list of input nodes (NOT layers), following some merge mode in the Functional API:

import com.intel.analytics.bigdl.dllib.keras.layers.Merge.merge

merge(inputs, mode = "sum", concatAxis = -1) // This will return an output NODE.

Parameters:

  • inputs: A list of node instances. Must be more than one node.

  • mode: Merge mode. String, must be one of: ‘sum’, ‘mul’, ‘concat’, ‘ave’, ‘cos’, ‘dot’, ‘max’. Default is ‘sum’.

  • concatAxis: Int, axis to use when concatenating nodes. Only specify this when merge mode is ‘concat’. Default is -1, meaning the last axis of the input.

Example code to create a graph model:

import com.intel.analytics.bigdl.dllib.keras.layers.{Dense, Input}
import com.intel.analytics.bigdl.dllib.keras.layers.Merge.merge
import com.intel.analytics.bigdl.dllib.keras.models.Model
import com.intel.analytics.bigdl.dllib.utils.Shape

// instantiate input nodes
val input1 = Input[Float](inputShape = Shape(8))
val input2 = Input[Float](inputShape = Shape(6))
// call inputs() with an input node and get an output node
val dense1 = Dense[Float](10).inputs(input1)
val dense2 = Dense[Float](10).inputs(input2)
// merge two nodes following some merge mode
val output = merge(inputs = List(dense1, dense2), mode = "sum")
// create a graph container
val model = Model[Float](Array(input1, input2), output)

7. Persistence#

This section describes how to save and load the Keras-like API.

7.1 save#

To save a Keras model, you call the method saveModel(path).

Scala:

import com.intel.analytics.bigdl.dllib.keras.layers.{Dense, Activation}
import com.intel.analytics.bigdl.dllib.keras.models.Sequential

val model = Sequential[Float]()
model.add(Dense[Float](32, inputShape = Shape(128)))
model.add(Activation[Float]("relu"))
model.saveModel("/tmp/seq.model")

Python:

import bigdl.dllib.keras.Sequential
from bigdl.dllib.keras.layer import Dense

model = Sequential()
model.add(Dense(input_shape=(32, )))
model.saveModel("/tmp/seq.model")

7.2 load#

To load a saved Keras model, you call the method load_model(path).

Scala:

import com.intel.analytics.bigdl.dllib.keras.Models

val model = Models.loadModel[Float]("/tmp/seq.model")

Python:

from bigdl.dllib.keras.models
model = load_model("/tmp/seq.model")