Incidence Matrix Build

Problem

Build the oriented incidence matrix B of an undirected graph: rows are vertices and columns are edges.

For edge e = (a, b), set B[a][e] = -1 and B[b][e] = 1, and leave all other entries 0.

Hint

Each column has exactly one +1 and one -1, so the all-ones vector is always in its left null space.

case 1

in: [3,[[0,1],[1,2]]]

expected: [[-1,0],[1,-1],[0,1]]

case 2

in: [2,[[0,1]]]

expected: [[-1],[1]]

case 3

in: [3,[[0,1],[0,2],[1,2]]]

expected: [[-1,-1,0],[1,0,-1],[0,1,1]]

case 4

in: [3,[[0,2]]]

expected: [[-1],[0],[1]]

Starter codePython

def incidence_matrix(num_vertices, edges):
    # Your code here
    pass

4 test cases · run your code against them in the editor