<｜begin▁of▁sentence｜>### Instruction:
As a networkx expert, you might be working on analyzing the connections between different types of respiratory disorders for a medical research project. In this scenario, you may need to write a network representing the relationships between different conditions to a file in .ncol format in order to share and collaborate with other researchers.
### Response:
from igraph import Graph

# Create a simple graph
vertices = ['A', 'B', 'C', 'D']
edges = [(0, 1), (0, 2), (2, 3)]

# Instantiate the Graph
g = Graph(vertex_attrs={'label': vertices}, edges=edges, directed=False)

# Write graph to a file in .ncol format
g.write_ncol('graph.ncol')
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