MathDB
Tropical quadratics

Source: Canada Repêchage 2017/4

April 13, 2017
algebratropical geometryquadratics

Problem Statement

In this question we re-define the operations addition and multiplication as follows: a+ba + b is defined as the minimum of aa and bb, while aba * b is defined to be the sum of aa and bb. For example, 3+4=33+4 = 3, 34=73*4 = 7, and 342+54+7=min(3 plus 4 plus 4,5 plus 4,7)=min(11,9,7)=7.3*4^2+5*4+7 = \min(\text{3 plus 4 plus 4}, \text{5 plus 4}, 7) = \min(11, 9, 7) = 7. Let a,b,ca, b, c be real numbers. Characterize, in terms of a,b,ca, b, c, what the graph of y=ax2+bx+cy = ax^2+bx+c looks like.