rcd@opus.UUCP (Dick Dunn) (07/03/84)
>All of this discussion of the merits of Fortran vs. C seems to be missing one >of the most important points of all: ACCURACY. > >My point is not that C is inherently inaccurate... >...I would count on the >people at Cray to do the best job possible; after all, it's their bread and >butter... Perhaps you haven't seen some of the bizarre phenomena that have come from Mr. Cray. The Cray I has no divide instruction; instead it has a reciprocal approximation (emphasis on "approximation"). Try that one for numerical analysis. Or how about his earlier designs, the 6600 and family? The rounded floating add/subtract round the operands rather than the result. The rounded divide is even more exotic; in effect the result is rounded by either 1/3 or 2/3, depending on whether a final shift is required to normalize the result. I haven't had any opportunity to look at the software since old CDC 6x00 days (late 60's for me), but at that time the software matched the hardware in numerical soundness. In other words, don't believe what the salesmen tell you. Don't even believe what you might think ought to be true. Check it out carefully (and cynically). Array-processor companies like Floating Point Systems and Sky Computer tend to produce stuff that is as trustworthy as Cray's, simply because nothing is quite so embarrassing as selling a number-crunching machine that squashes the results. I hope I haven't come across as a snooty know-it-all. The fact is that I am aware of these problems precisely because I learned the hard way that I *don't* know a damned thing about numerical mathematics. No apology--it's not even close to my specialty and nobody can follow everything. When I need to do real math, I find me an expert. -- Dick Dunn {hao,ucbvax,allegra}!nbires!rcd (303)444-5710 x3086 ...Never attribute to malice what can be explained by stupidity.
rcd@opus.UUCP (Dick Dunn) (07/04/84)
Silly editor games! I mistakenly left a dozen or more lines of the parent article (174@callan) on the end of mine (to which this is a followup). Sorry, particularly to the author of the original article. -- Dick Dunn {hao,ucbvax,allegra}!nbires!rcd (303)444-5710 x3086 ...Never attribute to malice what can be explained by stupidity.
rcd@opus.UUCP (Dick Dunn) (07/04/84)
Please ignore the article 586@opus (same title). Here's the un-messed-up version (assuming I can get it put together and get out of the editor without any more fumbles. >All of this discussion of the merits of Fortran vs. C seems to be missing one >of the most important points of all: ACCURACY. > >My point is not that C is inherently inaccurate... >...I would count on the >people at Cray to do the best job possible; after all, it's their bread and >butter... Perhaps you haven't seen some of the bizarre phenomena that have come from Mr. Cray. The Cray I has no divide instruction; instead it has a reciprocal approximation (emphasis on "approximation"). Try that one for numerical analysis. Or how about his earlier designs, the 6600 and family? The rounded floating add/subtract round the operands rather than the result. The rounded divide is even more exotic; in effect the result is rounded by either 1/3 or 2/3, depending on whether a final shift is required to normalize the result. I haven't had any opportunity to look at the software since old CDC 6x00 days (late 60's for me), but at that time the software matched the hardware in numerical soundness. In other words, don't believe what the salesmen tell you. Don't even believe what you might think ought to be true. Check it out carefully (and cynically). -- Dick Dunn {hao,ucbvax,allegra}!nbires!rcd (303)444-5710 x3086 ...Never attribute to malice what can be explained by stupidity.
yba@mit-athena.ARPA (Mark H Levine) (07/11/84)
Come on you guys. Everybody knows that a good lisp has arbitrary (arbitrarily high) precison, accuracy, and better speed than Fortran. What's to debate? -- yba%mit-heracles@mit-mc.ARPA UUCP: decvax!mit-athena!yba