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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def incidence(self):
 """Build incidence matrix into self.C"""

        self.C = \
            spmatrix(self.u, range(self.n), self.a1, (self.n, self.nb), 'd') -\
            spmatrix(self.u, range(self.n), self.a2, (self.n, self.nb), 'd')