Possible Duplicate:
Why does “convex function” mean “concave up”?
Forty years ago I recall seeing the definition of a convex function (ie, that the points on the line segment joining two points on its graph are above its graph), with the definition of a concave function being that its negative is convex. Now, teaching high school mathematics, I am seeing “concave up” used with the meaning of “convex”, and “concave down” to mean “concave”. I can sympathize with the strong intuitive basis of this high school terminology, but I was just wondering whether is goes beyond high school. For example, when you are “really” doing mathematics, you speak of, say, the concavity of the logarithm, right?, never its “concave-down-ness”, right?
added just before posting: I see that T.. has pretty much answered this already here on MSE at a related post. Here’s the link:
Why does "convex function" mean "concave *up*"?
If you all want to close this question of mine as a duplicate, I won’t mind.