Author: martin fierz
Date: 17:42:13 09/04/02
Go up one level in this thread
On September 04, 2002 at 20:16:00, Robert Hyatt wrote: >On September 04, 2002 at 19:22:25, martin fierz wrote: > >>On September 04, 2002 at 18:20:49, Terry Ripple wrote: >> >>>This is hardly the place to try and discredit our fellow CCC members and you >>>know who i'am refering to! This was very distasteful and uncalled for and >>>shouldn't have been allowed to continue at all. >>> >>>I just wanted to give my opinion on this matter! >>> >>>Regards, >>> Terry >> >>i disagree with you... bob's DTS paper has 2 major flaws with numbers: >>1. numbers in a table are claimed to be measured, and they are not, and vincent >>is absolutely right to point this out. >> >>2. bob's rounding of 1.81 to 1.9 and rounding the average of these rounded >>results can result in an average speedup of 1.82 to be reported as 2.0. this is >>ridiculous and any undergraduate student should not get away with something like >>that. > >I don't follow that point. Each "speedup" is computed from two numbers, >the N processor time divided into the one processor time. There is a >roundoff/truncation issue there. I didn't say "I did round up". I said >"it is possible that the log eater might have done that." > >But that only happened on a single speedup. There is no "second" roundup >because each speedup is only computed once. So for normal math, the error >is +/- .05. If I happened to have done it in integer math, then the error >_could_ have been +/- .09. Unfortunately, without the code, I can't say >which. I suspect it was pure floating point, using the %.1f type format, >which means .05 is the actual error. But that is just my best guess. Not >a statement of fact... well, on the famous page in question, you give speedups for every position in table 5, and then an average speedup in table 6. as far as i can see, table 6 is the main result of this paper, not table 5, right? i surely would not remember all 24 numbers, but i would remember that you claim to get a nice 2.0 speedup on a dual machine. IF you really rounded the way you might have done, you have two roundings. i can see that you computed 2.0 from the 24 single speedups, when the proper result would be 1.9583333... which you should give as 1.96, not as 2.0. obviously, IF you rounded the single speedups that way, then, on average you are giving a 0.05 too high speedup. if you subtract that, you get 1.91... which is kind of closer to 1.9 than 2.0... i am not saying this is a BIG MISTAKE which invalidates any conclusions or anything. it's just something you shouldn't do. it doesn't even matter if you did it or not - if you still think that that is a valid procedure, then you should think again :-) aloha martin
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