Archive for the ‘math’ Tag

Atrophy by Abstraction

In 1957, Isaac Asimov wrote a short story entitled “A Feeling of Power” about a future society where humans had lost to atrophy the ability to perform even simple arithmetic due to a total dependence on computers.  Now I could log volumes on the abysmal state of math knowledge in the humans wandering around in today’s society, but this piece isn’t about that.  It is however along parallel lines for software engineering.

I’ve been doing a fair amount of recruiting for my Engineering team this year and I’m happy to say I’ve hired great people, but it wasn’t easy.  One of the things I like about the process is that I learn a lot.  One of the things I hate is what I sometimes learn, like how many software engineers who have been working in object-oriented technologies for many years who can’t give a lucid explanation of encapsulation or inheritance; and abandon all hopes of polymorphism – log that knowledge as an exception.  These are the core pillars of object orientation and if you can’t at least describe them (much less define them), you can’t use them correctly.

For the most part, I’m not talking about young engineers right out of school, although you’d think they would have forgotten less.  I’m talking about the 5-10 year senior engineer who stares as still as a fallen log hoping that the gods of seniority will suddenly inspire unto them the fundamentals.  And on the subject of “senior” in the title, calling a squirrel a duck doesn’t make it quack.  Admittedly Shakespeare put it more eloquently, “A rose by any other name would smell as sweet.

Another favorite question of mine as my colleagues well know is the binary search.  I often ask engineering candidates, especially server-side and database types, to describe it relative to any other search technique.  Half the time the answer starts by naming certain Java classes – nope pull up, this is not a Java question.  Overall, about 1 in 5 does pretty well.  For the rest, I usually resort to playing a game.

I’m thinking of a number from 1 to 100.  You need to guess it in the fewest number of tries and after each, I will tell you that you’re either correct, too low, or too high.

Almost everyone figures out that the logical first guess is 50.  It has no more of a chance of being right than any other guess, but at least you’re reliably cutting the space in half.  If I say “too high”, then guess 25.  If I then say “too low”, then guess 37, and so on.  That’s a binary search!  Start with a sorted collection and find what you need by successively dividing the search space by 2.

Only once was someone’s first answer not 50 – they guessed 70 and my head exploded scattering debris for miles and miles.

I ask this question because knowing how things work matters.  If you don’t understand the binary search, for example, then you have no idea how an index helps a SQL select or why database inserts and updates are costly when indices are overused.  You may never have to code a binary search ever again thanks to abstraction and reuse, but just because something has been abstracted away from daily view doesn’t mean it isn’t executing at runtime.  Understanding this principle is crucial to being able to play in the high-scale league.

Folding a little math back into my binary search question, I usually ask the following just for fun since only about 1 in 50 come close.  Given a collection of size N, what is the worst case number of tries before you’re sure to win?  More blank fallen log stares as they try to play out the guessing game in their heads, so I lead them down the path.  If N = 2x (i.e., multiplying by 2, x times), then what is the inverse function x = f(N) (i.e., how many times can N be divided by 2)?  What is the inverse of exponent?  But this only helps 1 or 2 more out of 50.

If the many occurrences of the word “log” so far in this post weren’t enough of a clue…

If N = 2x, then x = log2 N

Stealing a bit from Bill Maher and his HBO series, I think we need some New Rules:

  1. All programmers are not engineers.  Programmers write computer programs, maybe even really good ones.  But to be an engineer, one has to know how things work or at least possess the intellectual curiosity to want to know.
  2. Calendars and titles do not make engineers senior.  Few things raise my resume red flags higher than seeing every position since kindergarten as Senior this, Lead that, or Super-Duper something else.  Take the time to learn your craft.  That will distinguish you.
  3. Abstraction without fundamentals is unstable.  It can cause us to mistake tight source code for code that performs well, not thinking about the mass of code sitting in base classes, libraries, and frameworks.  We can write resource-sloppy code and assume the garbage collector will magically clean up behind us.  Try that at scale.

Summing up, abstraction is good.  It has marked the forward movement of software engineering for many decades.  It drives productivity and at least potentially drives better designs, testability, extensibility, maintainability, and lots of other good characteristics.  But it can also give us permission to be lazy.  With or without title qualifiers, good engineers do not let this happen.  They are self motivated to learn and they learn deep, not just broad.

Well, I’ve given away a few of my favorite interview questions here, but if my upcoming candidates suddenly know these answers, I can at least give them credit for reading the interviewer’s blog as preparation.


New Math

Reductionism, the philosophical position that a complex system is nothing other than the sum of its parts, has largely fallen out of favor and for good reason.  Quantum physics and phenomena such as chaos theory and emergent network effects have effectively closed the book on the notion that truth can be found by setting aside the whole and just analyzing fundamental elements.

Given this preamble, I was recently reminded of a pretty cool algebra trick that I first came across about 15 years ago.  Starting with a = b as a given, this series of simple algebraic manipulations proves that 1 = 2; a principle I wish I could apply to my 401k.

a  =  b
ab  =  b2
ab – a2  =  b2 – a2
a(b – a)  =  (b – a)(b + a)
a  =  b + a
a  =  a + a
a  =  2a
1  =  2

Clearly there’s a problem.  For readers who have not seen this and want to solve it, I’ll offer the following assurance without being a spoiler.  There is nothing lame here.  There are no hidden assumptions like this only works if you’re a subatomic particle or if you redefine the symbology of numbers.  The problem is simple and includes everything you need to know.

The frustrating part about this problem is that each individual step from one expression to the next is impeccable in its correctness, but ultimately 1 cannot equal 2.  There is of course an explanation, but it cannot be found solely in the exhaustive analysis of each step.

There is no profound moral to this post; just an observation that connecting dots can be more rewarding than just knowing each dot on a first name basis.  Said another way, if you’re beating your head against a wall because you don’t know where to go, try stepping back and reading the sign.