You're given a rectangle represented by a matrix. Implement functions to update values within specified subrectangles and retrieve the value at a given coordinate.

Imagine you're standing at a fixed location looking at points on a 2D plane. Determine the maximum number of points you can see within a given field of view by rotating your position.

You are given equations represented by pairs of variables and their corresponding values. Your task is to evaluate queries based on these equations, determining the value of expressions if possible, or returning -1.0 if not.