文摘
Consider a system of two polynomial equations in two variables: $$\begin{aligned} F(X,Y)=G(X,Y)=0, \end{aligned}$$ where \(F \in \mathbb {R}[X,Y]\) has degree \(d \ge 1\) and \(G \in \mathbb {R}[X,Y]\) has \(t\) monomials. We show that the system has only \(O(d^3t+d^2t^3)\) real solutions when it has a finite number of real solutions. This is the first polynomial bound for this problem. In particular, the bounds coming from the theory of fewnomials are exponential in \(t\) , and count only non-degenerate solutions. More generally, we show that if the set of solutions is infinite, it still has at most \(O(d^3t+d^2t^3)\) connected components. By contrast, the following question seems to be open: if \(F\) and \(G\) have at most \(t\) monomials, is the number of (non-degenerate) solutions polynomial in \(t\) ? The authors-interest for these problems was sparked by connections between lower bounds in algebraic complexity theory and upper bounds on the number of real roots of “sparse like-polynomials.