Mailman 3 September 2001 - NumPy-Discussion

re: gcc 3.0 vs. 2.95.2
by Peter Soendergaard 16 Sep '01

16 Sep '01

Hello, I just browsed over the archives for Numpy-discussion and saw this, and decided to sign up. I work on the ATLAS-project http://math-atlas.sourceforge.net/ and we have had similar problems with gcc3.0 Gcc 3.0 has a completely new backend which produces much slower floating point code on i386 machines. It is most visible on the Athlon, but it also also shows on on P4 and PIII machines. We havn't yet figured out if there are some optimizations that can make this go away, but if you need performance stick with the old 2.95 release for now. By the way, if you would like to use Atlas in NumPy (I don't know if you do it already) I might be of some help. There is c-interfaces to the BLAS bundled with ATLAS, supporting both row-major and column-major storage. Cheers, Peter.

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Re: PEP proposal for round(x,n) enhancement
by Christopher Smith 15 Sep '01

15 Sep '01

To Chris and others interested, Would you mind giving me an opinion here? I think you made the best argument for not using the name "round" since floating n is already accepted by round and changing how n is interpreted would break anyone's code who passed in n with a non-zero decimal portion. Sigfig or chop is an alternative but I really don't like the name "chop" since it's not descriptive of the rounding that takes place. Sigfig is ok, but I am proposing a round function (below) that offers more than just sigfigs. So...how about "round2" which has precedence in the atan2() function. The two sorts of roundings that can be done with round2() are 1) rounding to a specified number of significant figures or 2) rounding to the nearest "x". The latter is useful if you are making a histogram, for example, where experimental data values may all be distinct but when the deviation of values is considered it makes sense to round the observations to a specified uncertainty, e.g. if two values differ by less than sigma then they could be considered to be part of the same "bin". The script is below. Thanks for any input, /c #### from math import floor,log10 def round2(x,n=0,sigs4n=1): '''Return x rounded to the specified number of significant digits, n, as counted from the first non-zero digit. If n=0 (the default value for round2) then the magnitude of the number will be returned (e.g. round2(12) returns 10.0). If n<0 then x will be rounded to the nearest multiple of n which, by default, will be rounded to 1 digit (e.g. round2(1.23,-.28) will round 1.23 to the nearest multiple of 0.3. Regardless of n, if x=0, 0 will be returned.''' if x==0: return x if n<0: n=round2(-n,sigs4n) return n*int(x/n+.5) if n==0: return 10.**(int(floor(log10(abs(x))))) return round(x,int(n)-1-int(floor(log10(abs(x))))) ####

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A proposal for a round(x,n) enhancement
by Christopher Smith 12 Sep '01

12 Sep '01

Hello, I would like to see an addition to the round(x,n) function syntax that would allow one to specify that x should be rounded to the nth significant digit as opposed to the nth digit to the left or right of the 1's digit. I am testing the waters right now on python-list and have not yet submitted a PEP. Some there have suggested that it be called a different function. Someone else has suggested that perhaps it could be added into SciPy or Numeric as a function there. I prefer the name round because it describes what you are doing. Someone suggested that MATLAB has a function called chop that does what I am proposing and at http://www.math.colostate.edu/~tavener/M561/lab5/lab5.pdf the document says that the "MATLAB function chop(x,n) rounds (not chops!) the number x to n significant digits." If this new function was called "chop" then any previous MATLAB users would know what to expect. (But why call it chop if you are actually rounding?) What I think would be nice is to modify round so it can round to a given number of sig. figs. Here is a def called Round that simulates what I am proposing: from math import floor,log10 def Round(x,n=0): if n%1: d=int(10*n) return round(x,d-1-int(floor(log10(abs(x))))) else: return round(x,n) print Round(1.23456,2) #returns 1.23 print Round(1.23456,0.2) #returns 1.2 The way that I have enhanced round's syntax is to have it check to see if there is a non-zero decimal part to n. If there is, n is multiplied by 10 and the resulting value is used to compute which digit to round x to. n=0.1 will round to the first significant digit while n=0.4 and n=1.1 will round to the 4th and 11th, respectively. I don't believe you will run into any numerical issues since even though something like .3 may be represented internally as 0.29999999999999999, multiplying it by 10 gets you back to 3 and this value is what is used in the call to round() I am open to comments about implementation and function name. /c

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Precision
by Herbert L. Roitblat 11 Sep '01

11 Sep '01

I have been wanting use Float128 numbers on an Alpha system running Linux and Python 2.0. Float128 does not seem to be available. At least Float128 is undefined. Is the Alpha capable of support Float128 numbers? If it is, what am I missing to do be able to use it? Thanks, Herb

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Dynamic loading and shared libraries article
by Paul F. Dubois 11 Sep '01

11 Sep '01

My column this month has a really great article by David Beazley and two colleagues about how dynamic loading and shared libraries actually work and some things you can do with it. It is Computing in Science and Engineering, Sept/Oct 2001, Scientific Programming Department. I found the article a really big help in understanding this stuff. The magazine's web site is http://computer.org/cise. Paul

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ToyFDTDpython on Freshmeat yesterday
by Rob 11 Sep '01

11 Sep '01

>From my web statistics it looks like about 100 people downloaded it. Should give Numpy a pretty good showing as I got it running almost as fast as C. Only slowdown was dumping the E fields into a file every few ticks to generate the movie. I know there must be better ways to dump an array than use indexing- but I was so excited when I finally got it to near C speeds that I just let it be. Rob. -- The Numeric Python EM Project www.members.home.net/europax

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unwrap_function
by Karshi Hasanov 10 Sep '01

10 Sep '01

Hi all, Does NumPy provide "unwrap" function like in MatLab?

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Is there some method to realize qr decompostion
by wqh 09 Sep '01

09 Sep '01

I find through the doc ,but can not find any.What Numpy support compare with matlab is too few,can I think we must work hard to make it better. IP卡、上网卡两折史奴比、蜡笔小新全家福加入书友会获精美礼品

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can I use symbolic computation with numpy?
by wqh 06 Sep '01

06 Sep '01

I should use this ,but do not know how, if it can not,then which should I use to perform.thanks IP卡、上网卡两折史奴比、蜡笔小新全家福加入书友会获精美礼品

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Numeric 20.2.0 available in CVS or tar form
by Paul F. Dubois 06 Sep '01

06 Sep '01

Numeric 20.2.0 is available at Sourceforge or via cvs. The tag for cvs is r20_2_0. I haven't done the Windows installers yet.

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