ALGOPY features a simple code tracer. A trace of the executed code is necessary for the reverse mode of AD. The basic idea is to wrap an object x in an algopy.Function instance. Performing operations with Function instances are recorded in a computational graph, implemented in algopy.CGraph.

For example:

```
>>> import numpy
>>> from algopy import CGraph, Function
>>> cg = CGraph()
>>> cg.trace_on()
>>> x = Function(1)
>>> y = Function(3)
>>> z = x * y + x
>>> cg.trace_off()
>>> cg.independentFunctionList = [x,y]
>>> cg.dependentFunctionList = [z]
>>> print cg
>>> cg.plot('example_tracer_cgraph.png')
Id: IDs: 0 <- [0]
x:
1
Id: IDs: 1 <- [1]
x:
3
__mul__: IDs: 2 <- [0, 1]
x:
3
__add__: IDs: 3 <- [2, 0]
x:
4
Independent Function List:
[0, 1]
Dependent Function List:
[3]
```

and the plotted computational graph is: