Prevent errors or fix errors

Posted on 13 September 2014 by John

The other day I was driving by our veterinarian’s office and saw that the marquee said something like “Prevention is less expensive than treatment.” That’s sometimes true, but certainly not always.

This evening I ran across a couple lines from Ed Catmull that are more accurate than the vet’s quote.

Do not fall for the illusion that by preventing errors, you won’t have errors to fix. The truth is, the cost of preventing errors is often far greater than the cost of fixing them.

From Creativity, Inc.

What would Donald Knuth do?

Posted on 12 August 2014 by John

I’ve seen exhortations to think like Leonardo da Vinci or Albert Einstein, but these leave me cold. I can’t imagine thinking like either of these men. But here are a few famous people I could imagine emulating when trying to solve a problem

What would Donald Knuth do? Do a depth-first search on all technologies that might be relevant, and write a series of large, beautiful, well-written books about it all.

What would Alexander Grothendieck do? Develop a new field of mathematics that solves the problem as a trivial special case.

What would Richard Stallman do? Create a text editor so powerful that, although it doesn’t solve your problem, it does allow you to solve your problem by writing a macro and a few lines of Lisp.

What would Larry Wall do? Bang randomly on the keyboard and save the results to a file. Then write a language in which the file is a program that solves your problem.

What would you add to the list?

Sometimes definitions are enough

Posted on 16 May 2014 by John

Sometimes you can apply math just by raiding it for vocabulary. You may not need to apply a single theorem.

This has been a surprise to me. I’m more used to creating a mathematical model so you can compute something or apply some theorem. But sometimes you can move a project along just by providing a name for a concept. A meandering discussion can snap into focus because someone has a name for an idea everyone vaguely understands.

Sometimes it may be clear that only part of a mathematical definition applies. In this case math can guide the discussion by asking whether the rest of the definition applies. “It sounds like we’ve got a widget here. A widget has to have these five properties and clearly we have the first three. Let’s think about whether the last two hold.” The answers don’t have to be positive to be useful. You might realize something important in the process of explaining why your thing is not a widget.

Sometimes a definition may not apply at all and still be useful! “This reminds me of a widget. It’s not a widget in any strict sense. But if it were, this is what we’d do next. I wonder whether we can do something like that.”

Mental callouses

Posted on 17 February 2014 by John

In describing writing his second book, Tom Leinster says

… I’m older and, I hope, more able to cope with stress: just as carpenters get calloused hands that make them insensitive to small abrasions, I like to imagine that academics get calloused minds that allow them not to be bothered by small stresses and strains.

Mental callouses are an interesting metaphor. Without the context above, “calloused minds” would have a negative connotation. We say people are calloused or insensitive if they are unconcerned for other people, but Leinster is writing of people unperturbed by distractions.

You could read the quote above as implying that only academics develop mental discipline, though I’m sure that’s not what was intended. Leinster is writing a personal post about the process of writing books. He’s an academic, and so he speaks of academics.

Not only do carpenters become more tolerant of minor abrasions, they also become better at avoiding them. I’m not sure that I’m becoming more tolerant of stress and distractions as I get older, but I do think I’m getting a little better at anticipating and avoiding stress and distractions.

“I got the easy ones wrong”

Posted on 6 November 2013 by John

This morning my daughter told me that she did well on a spelling test, but she got the easiest words wrong. Of course that’s not exactly true. The words that are hardest for her to spell are the ones she in fact did not spell correctly. She probably meant that she missed the words she felt should have been easy. Maybe they were short words. Children can be intimidated by long words, even though long words tend to be more regular and thus easier to spell.

Our perceptions of what is easy are often upside-down. We feel that some things should be easy even though our experience tells us otherwise.

Sometimes the trickiest parts of a subject come first, but we think that because they come first they should be easy. For example, force-body diagrams come at the beginning of an introductory physics class, but they can be hard to get right. Newton didn’t always get them right. More advanced physics, say celestial mechanics, is in some ways easier, or at least less error-prone.

“Elementary” and “easy” are not the same. Sometimes they’re opposites. Getting off the ground, so to speak, may be a lot harder than flying.

Hard-working lazy people

Posted on 4 November 2013 by John

“It was a favorite theme of C. S. Lewis that only lazy people work hard. By lazily abdicating the essential work of deciding and directing, establishing values and setting goals, other people do it for us; then we find ourselves frantically, at the last minute, trying to satisfy a half dozen demands on our time, none of which is essential to our vocation, to stave off the disaster of disappointing someone.” — Eugene Peterson

Remove noise, remove signal

Posted on 28 October 2013 by John

Whenever you remove noise, you also remove at least some signal. Ideally you can remove a large portion of the noise and a small portion of the signal, but there’s always a trade-off between the two. Averaging things makes them more average.

Statistics has the related idea of bias-variance trade-off. An unfiltered signal has low bias but high variance. Filtering reduces the variance but introduces bias.

If you have a crackly recording, you want to remove the crackling and leave the music. If you do it well, you can remove most of the crackling effect and reveal the music, but the music signal will be slightly diminished. If you filter too aggressively, you’ll get rid of more noise, but create a dull version of the music. In the extreme, you get a single hum that’s the average of the entire recording.

This is a metaphor for life. If you only value your own opinion, you’re an idiot in the oldest sense of the word, someone in his or her own world. Your work may have a strong signal, but it also has a lot of noise. Getting even one outside opinion greatly cuts down on the noise. But it also cuts down on the signal to some extent. If you get too many opinions, the noise may be gone and the signal with it. Trying to please too many people leads to work that is offensively bland.

Related post: The cult of average

The difference between machines and tools

Posted on 14 September 2013 by John

From “The Inheritance of Tools” by Scott Russell Sanders:

I had botched a great many pieces of wood before I mastered the right angle with a saw, botched even more before I learned to miter a joint. The knowledge of these things resides in my hands and eyes and the webwork of muscles, not in the tools. There are machines for sale—powered miter boxes and radial arm saws, for instance—that will enable any casual soul to cut proper angles in boards. The skill is invested in the gadget instead of the person who uses it, and this is what distinguishes a machine from a tool.

Related post: Software exoskeletons

Tragedies and messes

Posted on 28 August 2013 by John

Dorothy Parker said “It’s not the tragedies that kill us; it’s the messes.”

Sometime that’s how I feel about computing. I think of messes such as having to remember that arc tangent is atan in R and Python, but arctan in NumPy and a in bc. Or that C, Python, and Perl use else if, elif, and elsif respectively. Or did I switch those last two?

These trivial but innumerable messes keep us from devoting our full energy to bigger problems.

One way to reduce these messes is to use fewer tools. Then you know less to be confused about. If you only use Python, for example, then elif is just how it is. But knowing more tools is worth the added mess, up to a point. Past some point, however, new tools add more mental burden than utility. You have to find the optimal combination of tools for yourself, and that combination will change over time.

To use fewer tools, you may need to use more complex tools. Maybe you can replace a list of moderately complex but inconsistent tools with one tool that is more complex but internally consistent.

Maybe you’re doing more than you need to

Posted on 28 May 2013 by John

Suppose a = 2485144657 and b = 7751389993.

What is the last digit of a*b?
What is the median digit of a*b?

In both questions it is conceptually necessary to compute a*b, but not logically necessary. Both are a question about a*b, so computing the product is conceptually necessary. But there is no logical necessity to actually compute a*b in order to answer a question about it.

In the first question, there’s an obvious short cut: multiply the last two digits and see that the last digit of the product must be 1.

In the second question, it is conceivable that there is some way to find the median digit that is less work than computing a*b first, though I don’t see how. Conceptually, you need to find the digits that make up a*b, sort them, and select the one in the middle. But it is conceivable, for example, that there is some way to find the digits of a*b that is less work than finding them in the right order, i.e. computing a*b.

I brought up the example above to use it as a metaphor.

In your work, how can you tell whether a problem is more like the first question or the second? Are you presuming you have to do something that you don’t? Are you assuming something is logically necessary when it is only conceptually necessary?

When I’m stuck on a problem, I often ask myself whether I really need to do what I assume I need to do. Sometimes that helps me get unstuck.