<｜begin▁of▁sentence｜>### Instruction:
As a financial planner, you're tasked with ensuring your clients' financial stability and security. Imagine you're working with a client who has diversified investments across various sectors represented by a network graph. In this graph, each vertex corresponds to a specific investment category, and edges denote the flow of funds between these categories. For instance, vertices 0, 1, 2, and 3 represent different sectors like technology, healthcare, energy, and real estate, respectively. The edges {(0, 1), (1, 2), (2, 3)} indicate the interconnection of investments between these sectors.

To maintain a comprehensive record of your client's investment network, you aim to save this graph in a Pajek format file called 'output.net'. You plan to utilize the `write_pajek` function provided by the igraph API, a tool you often rely on for managing and analyzing investment data. This process ensures that you have a structured representation of your client's investment portfolio, facilitating further analysis and decision-making to optimize their financial goals.
### Response:
import igraph as ig

# Initialize a graph
g = ig.Graph([(0, 1), (1, 2), (2, 3)])

# Write the graph to a Pajek .net file
g.write_pajek('output.net')
<|EOT|>
