The Lumber Room

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Convex and concave

with 6 comments

A mnemonic for ‘convex’ and ‘concave’:

Convex

A convex function

conCAVE

A conCAVE function

Two mnemonics are better than one.

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Written by S

Tue, 2009-03-17 at 15:56:28 +05:30

Posted in Uncategorized

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6 Responses

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  1. Oh yeah? I guarantee that at least one student will remember it like this and get it exactly wrong:

    concaVe (with a big V)

    Convex (with a big C)

    boo

    Tue, 2009-03-17 at 16:10:45 +05:30

    Reply

    • Heh, personal mnemonics often have that problem. :)

      I associate “convex” and not “concave” with the “v” sound (it’s the first letter where they’re different, so the words are really “vex” and “cave”), so it works for me. If I thought of the “big C”, I would probably reason that it the “c” can go with either word, and “concave” has a better claim on it.

      I see your point, though… one should always devise one’s own mnemonics; others’ will only confuse.

      Shreevatsa

      Tue, 2009-03-17 at 16:16:56 +05:30

      Reply

  2. In the chapter named “Los Alamos from Below” in Surely You’re Joking…, Feynman describes what the view was like “from the bottom”, his metaphor for working as hands-on as he could, having immersed himself entirely in his work.

    I read this book at the same time I had a real analysis course in college, and owing to some illogical association-by-simultaneity conflation, I came to differentiate convex and concave functions by “viewing from the bottom” (i.e. literally). Never had trouble with the definitions since.

    To each his own, I guess. Mnemonics are funny constructs.

    Anonymous

    Tue, 2009-03-17 at 18:26:17 +05:30

    Reply

    • Ah right, that would work too. These days I seldom encounter “convex” and “concave” in their natural-world meanings; it is usually in a mathematical context. So I didn’t even understand your mnemonic at first; maybe some day I’ll need a mnemonic for remembering which means ‘bulging outward / toward you’ and which means the other. :)

      Shreevatsa

      Wed, 2009-03-18 at 00:36:05 +05:30

      Reply

  4. [...] convex function (need a mnemonic?) is such that for any λ in [...]

    Convex, continuous, Jensen’s « The Lumber Room

    Tue, 2010-06-29 at 03:46:05 +05:30

    Reply

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