Embedded Systems December 2000 Vol13_13

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Jack W. Crenshaw Oops! I Did It Again If you 're wondering where I was last month, I was taking a much-needed vacation. I used the time to go out to San Jose for the Embedded Systems Conference. Among other things, I did a book signing for my new book (shameless plug), Math Toolkit for Real- Time Programming. 1 I'll bet you can never gues where the mate rial for it came from. A few readers dropped by to say hello and listened to J ean Labros e and me try to talk them into buying our books. It was good to see you aJl. I have a lot to say about the ESC, mainly that it was hugel If you've never attended one of these confe r- ences, you really owe it to yourself to do so. Beg, plead, and caj ole your boss to send you, or just pony up the money on your own. But get there! If you' re like me, you' ll find its atmos- phe re of excitement and change a cure for every caught-in-a-rut feeling you've ever had. Exciting th ings a re going on. I'll have a lot more to say about the conference and other things, such as my occasional Good Guys/ Bad Guys list. But this month I want to dive right into the minimization problem. So I'll defer the rest, except for these two comments. First, I had speculated in an earlier column that large companies nowa- days practice "planned disgruntle- ment," meaning tll at they optimize their tech support to save costs by intentionally aJienating a certain per- centage of customers. A reader (who I'll keep anonymous, along witll the company he names, to avoid any repercussions) sent me the fo llowing e-mail, under the heading, "Suspicions confirmed": 'Jack, I want to confirm your belief that companies do exactly what you think about QA on their products. During tlle '80s, I learned that none less than [Company X, a very large, very prestigious company, noted for its quaJi ty] formally used a way to reduce testing on new products even if it Second, a reader, Mike Mullen, was kind enough to send me his personal copy of Brent's book, Algorithms for Minimization Without Derivatives.2 Was that generous or what? A cursory glance goes a long ways towards explaining why nobody ever seems to explain how Brent's metllod works. It's the same reason why everyone quotes, but very few people ever actu- ally read, Kalman's paper on Kalman Jack returns from holiday refreshed and ready to solve the problem of minimization once and for all. meant losing some customers. This was factored into their cost of doing busin ess. This was documented in a paper in an obscure statistics proceed- ings conference paper in [deleted] during the mid '80s. I didn 't believe this when a [Company X] sale man told me. It took our tech libra.], [Company Y] some time to find it." To this I will add an observation from a colleague, who noted that he seemed to be getting a lot of dead-on- arrival items from a large department store tllat has a reputation for .'eplac- ing broken items, no questions asked. After some sleuth ing, he concluded that the company had made this poli- cy possible by skipping acceptan ce testing on their products. In effect, they're using tlleir customers as their QA department. Interesting concept. filtering, or Cooley's pape.'s on Fast Fourier Transforms. Brent is a mathe- matician, and mathematicians, ble s 'em, think in terms of theorems and lemmas. Such words tend to make my eyes cross in the same way that some of my stuff on matrices or quaternions does for you readers out tllere. Even more to the point, and most astonishingly, eve n Brent doesn ' t explain Bre nt's algorithm! That's right, you read correctly. After going through aJl sorts of proofs of guaran- teed superl inear performance and the effects of round-off, Brent just sort of plops his algorithm out tllere, with no explanation whatsoever. 0 wonder Press et al. didn't explain it!3 They had nothing from which to work. This puts us all in a strange situa- tion, it seems to me. The algoritllm seems to have proven itself, and has been adopted by most of the scientific Embedded Systems Programming DECEMBER 2000 15

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