Identify convex and concave parts of polygon

c = convex([x,y]) c = 1 where the polygon curves toward the interior c = -1 where the polygon curves outwards

This function can be used to identify convex and concave parts of a polygon, such as the airfoil profile in the figure.

Thanks to Luigi Ventre who posed the problem in a comment to File Exchange entry Curvature of a 1D curve in a 2D or 3D space.