The easiest way to understand how this all fits together is by building a simple example.

To start, let's implement a simple graph to add two numbers together—basically, this would be: c = a + b:

1. First, let's import some libraries—most importantly, Gorgonia, as follows:

package main
import (
     "fmt"
     "log"
     . "gorgonia.org/gorgonia"
 )

2. Then, let's start our main function, like so:

func main() {
  g := NewGraph()
}

3. To that, let's add our scalars, as shown here:

a = NewScalar(g, Float64, WithName("a"))
b = NewScalar(g, Float64, WithName("b"))

4. Then, very importantly, let's define our operation node, as follows:

c, err = Add(a, b)
if err != nil {
              log.Fatal(err)
              }

Note that c will not actually have a value now; we've just defined a new node of our computation graph, so we need to execute it before it will have a value.

5. To execute it, we need to create a virtual machine object for it to run in, as follows:

machine := NewTapeMachine(g)

6. Then, set the initial values of a and b, and proceed to get the machine to execute our graph, as shown here:

Let(a, 1.0)
Let(b, 2.0)
if machine.RunAll() != nil {
                           log.Fatal(err)
                           }

The complete code is as follows:

package main

import (
         "fmt"
         "log"

         . "gorgonia.org/gorgonia"
)

func main() {
         g := NewGraph()

         var a, b, c *Node
         var err error

         // define the expression
         a = NewScalar(g, Float64, WithName("a"))
         b = NewScalar(g, Float64, WithName("b"))
         c, err = Add(a, b)
         if err != nil {
                  log.Fatal(err)
         }

         // create a VM to run the program on
         machine := NewTapeMachine(g)

         // set initial values then run
         Let(a, 1.0)
         Let(b, 2.0)
         if machine.RunAll() != nil {
                  log.Fatal(err)
         }

         fmt.Printf("%v", c.Value())
         // Output: 3.0
}

 Now, we have built our first computation graph in Gorgonia and executed it!