<｜begin▁of▁sentence｜>### Instruction:
Given a graph which you have constructed with vertices labeled 'a', 'b', 'c', 'd', and edges connecting these vertices in a square shape (each with an associated capacity), can you use the write_dimacs method to save this labeled and capacity-augmented graph to a file in DIMACS format, specifying the source as vertex 'a' (ID 0) and target as vertex 'd' (ID 3)?
### Response:
from igraph import Graph

# Create a graph
edges = [(0, 1), (1, 2), (2, 3), (3, 0)]
vertex_labels = ['a', 'b', 'c', 'd']
g = Graph(edges)
g.vs['label'] = vertex_labels # Assign labels to the vertices
g.es['capacity'] = [10, 10, 20, 20]  # Assign capacities to edges

# Write the graph to a DIMACS file
file_path = 'graph.dimacs'
g.write_dimacs(f=file_path, source=0, target=3, capacity='capacity')
<|EOT|>
