Concepts of Graphs in Tensorflow

In the world of Tensorflow, understanding the concept of computation graphs is crucial. A computation graph is a series of TensorFlow operations arranged into a graph of nodes. Each node takes zero or more tensors as inputs and produces a tensor as an output. It's a symbolic way of describing your mathematical operations and it's what gives TensorFlow its name.

Defining and Visualizing a Computation Graph

To define a computation graph in Tensorflow, you start by creating nodes. These nodes can be operations, variables, or even constants. For example, you could create two constant nodes and one operation node that adds the two constants together.

Here's a simple example:

import tensorflow as tf

# Define two constant nodes
node1 = tf.constant(3.0, dtype=tf.float32)
node2 = tf.constant(4.0) # also tf.float32 implicitly

# Define an operation node
node3 = tf.add(node1, node2)

In this example, node3 is an operation node that adds node1 and node2. The computation graph for this example would look like this:

node1 ----\
           \
            --> node3
           /
node2 ----/

To visualize a computation graph, you can use TensorBoard, a suite of visualization tools included with Tensorflow. TensorBoard will read TensorFlow events files, which contain summary data that you can generate when running TensorFlow.

The Role of Nodes and Edges in a Computation Graph

In a computation graph, nodes represent mathematical operations, while edges represent the tensors that flow between nodes.

Nodes are where the computation happens. They take in zero or more tensors as input, perform a mathematical operation, and output a tensor.

Edges, on the other hand, represent the tensors. Tensors are multi-dimensional arrays with a uniform type (float32, int32, or string, for example) and can be seen as the "data" in the computation graph that gets processed by the operation nodes.

Practical Examples of Creating and Executing Computation Graphs in Tensorflow

Let's expand on the previous example. To actually evaluate the nodes, we must run the computation graph within a session. A session encapsulates the control and state of the TensorFlow runtime.

Here's how you can create a session and run the computation graph:

# Create a session
sess = tf.Session()

# Run the computation graph
print(sess.run(node3))  # returns 7.0

In this example, sess.run(node3) triggers the execution of the computation graph and returns the result of the operation node node3.

Remember, Tensorflow computation graphs are a powerful concept that allows you to define complex mathematical operations and execute them efficiently. They are a fundamental part of how Tensorflow works under the hood.