Computing the topology of a real algebraic plane curve whose equation is not directly available

We present a collection of methods and tools for computing the topology of real algebraic plane curves de .ned by bivariate polynomial equations that are known at certain values or easy to evaluate, but whose explicit description is not available.The principal techniques used are the reduction of the computation of the real roots of the discriminant to a sparse generalized eigenvalue problem,the use of the structure of the nullspace of the classical Bezoutian, and its description in terms of the Lagrange Basis.