Convex and Concave [SEP] inception
Convex and Concave
Convex and Concave is a lithograph print by the Dutch artist M. C. Escher, first printed in March 1955.
It depicts an ornate architectural structure with many stairs, pillars and other shapes. The relative aspects of the objects in the image are distorted in such a way that many of the structure's features can be seen as both convex shapes and concave impressions. This is a very good example of Escher's mastery in creating illusions of "impossible architecture." The windows, roads, stairs and
Concave function
In mathematics, a concave function is the negative of a convex function. A concave function is also synonymously called concave downwards, concave down, convex upwards, convex cap or upper convex.
Definition.
A real-valued function formula_1 on an interval (or, more generally, a convex set in vector space) is said to be "concave" if, for any formula_2 and formula_3 in the interval and for any formula_4, 
A function is called "strictly concave" if
for any