NumPy-Discussion November 2008

numpy-discussion@python.org

105 participants
129 discussions

unpickle
by Frank Lagor 20 Nov '08

20 Nov '08

I have only used pickle a little and I did not see this in the docstring: Is there anyway to unpickle in reverse order? It appears the pickling works like a queue. I execute: pickle.dump(obj1,file) pickle.dump(obj2,file) Then when I go to retrieve: pickle.load(file) returns obj1 pickle.load(file) returns obj2 I am looking for a quick way to grab the last thing pickled (like a stack instead). Thanks in advance, Frank

2 2

Priority rules between 0d array and np.scalar
by Pierre GM 20 Nov '08

20 Nov '08

All, That time of a month again: could anybody (and I'm thinking about you in particular, Travis O.) can explain me what the priority rules are between a 0d ndarray and a np.scalar ? OK, I understand there are no real rules. However, the bug I was describing in a previous thread (www.mail-archive.com/numpy-discussion@scipy.org /msg13235.html) is still around: When multiplying/adding a np.scalar and ma.masked, the result varies depending on the order of the arguments as well as on their dtype. (Keep in mind that ma.masked is a subclass 0d ndarray of value 0 and dtype np.float64, with a __array_priority__ of 15). ma.masked * np.float32(1) => ma.masked np.float32(1) * ma.masked => ma.masked ma.masked * np.float64(1) => ma.masked np.floa64(1) * ma.masked => 0 My understanding is that for the first 2 operations, ma.masked takes over because it has the higher dtype. In that case, we use the rules defined in MaskedArray for multiplication (either __mul__ or __array_wrap__). For the 3rd and 4th operations, the two arguments have the same dtype and it looks like we're switching to a different priority rule. I would have expected ma.masked to take over in both cases, because a MaskedArray has a higher __array_priority__ than a ndarray or a np.scalar. That's not the case: the fact that ma.masked is a subclass of ndarray is not recognized... I hope I didn't lose anybody in my description. A ticket has recently been filled about the same issue: http://scipy.org/scipy/numpy/ticket/826 Looking forward to hearing from y'all P.

1 0

question about the documentation of linalg.solve
by Alan G Isaac 20 Nov '08

20 Nov '08

If if look at help(np.linalg.solve) I am told what it does but not how it does it. If I look at http://www.scipy.org/doc/numpy_api_docs/numpy.linalg.linalg.html#solve there is even less info. I'll guess the algorithm is Gaussian elimination, but how would I use the documentation to confirm this? (Shouldn't I be able to?) I don't think possible differences from the "lite" version are a reason for saying nothing... Thanks, Alan Isaac

6 10

Reduced row echelon form
by Robert Young 20 Nov '08

20 Nov '08

Hi, Is there a method in NumPy that reduces a matrix to it's reduced row echelon form? I'm brand new to both NumPy and linear algebra, and I'm not quite sure where to look. Thanks Rob

5 5

Re: [Numpy-discussion] glibc memory corruption when running numpy.test()
by Hoyt Koepke 20 Nov '08

20 Nov '08

Hi, Sorry; my first message wasn't under 40 KB with the attachments, so here's the same message but with the log files at http://www.stat.washington.edu/~hoytak/logs.tar.bz2. > Which ones ? Sorry; ATLAS = 3.9.4 and lapack=3.2. I'll give 3.8.2 a shot per your advice. > You should not do that, it won't work as you would expect. It is a good > rule to assume that you should never set the *FLAGS variable unless you > really know what you are doing. Fair enough. In my case I was having some issues with 32 bit and 64 bit mismatches (I think that fftw defaulted to 32 bit), so I set the flags variables. I also wanted to get the extra few percent of performance by using the tuning flags. I'll back up a bit now before playing with them now, though. > First, can you try without any blas/lapack (Do BLAS=None LAPACK=None > ATLAS=None python setup.py ....) ? This now works in the sense that it doesn't hang. I still get a number of test failures, however (build + test logs attached). Thanks a lot for the help! --Hoyt ++++++++++++++++++++++++++++++++++++++++++++++++ + Hoyt Koepke + University of Washington Department of Statistics + http://www.stat.washington.edu/~hoytak/ + hoytak(a)gmail.com ++++++++++++++++++++++++++++++++++++++++++

4 4

glibc memory corruption when running numpy.test()
by Hoyt Koepke 19 Nov '08

19 Nov '08

Hello, Sorry about this bug report.... I know how much us programmers like these kind of bugs :-/. In testing the latest svn version of numpy (6083), I get a memory corruption error: test_csingle (test_linalg.TestSolve) ... ok test_double (test_linalg.TestSolve) ... ok test_empty (test_linalg.TestSolve) ... ok Check that matrix type is preserved. ... ok Check that matrix type is preserved. ... ok test_nonarray (test_linalg.TestSolve) ... ok test_single (test_linalg.TestSolve) ... ok Ticket #652 ... *** glibc detected *** python: free(): invalid next size (fast): 0x0000000002c80ef0 *** ... and it hangs. I don't get any errors in my installation. The system is a 64bit intel xeon server running debian unstable, compiler is gcc-4.3.2 This *doesn't* happen with version 1.2.1. I do get some other test failures with that version, which I can post if you all think they are related, but they don't seem to be at first glance. I've attached the full log. If there is anything more you want me to do with this, I'd be happy to. Thanks! --Hoyt ++++++++++++++++++++++++++++++++++++++++++++++++ + Hoyt Koepke + University of Washington Department of Statistics + http://www.stat.washington.edu/~hoytak/ + hoytak(a)gmail.com ++++++++++++++++++++++++++++++++++++++++++

2 4

simple python question on what happens when functions are declared
by Frank Lagor 19 Nov '08

19 Nov '08

Hi, Can someone please explain what happens here: In testfile.py: x = 5 def arbFunc(): print x del x print "Done with Test" arbFunc() Then run the file with python testfile.py As opposed to x = 5 print x del x print "Done with Test" Which of course works fine. This question is of importance to me, because I may may very large arrays that strain the limits of the machine's memory and I need to clean up after myself when I generate other large objects temporarily. Thanks in advance! Frank

2 2

matio lib
by Neal Becker 19 Nov '08

19 Nov '08

A library for matlab io, perhaps this could be useful? http://sourceforge.net/projects/matio

1 0

convert pair of real arrays -> cmplx
by Neal Becker 19 Nov '08

19 Nov '08

What's the best way to convert a pair of real arrays representing real and imag parts to a complex array?

2 1

Memmapping .npy
by Gael Varoquaux 19 Nov '08

19 Nov '08

Currently memmapping a .npy file is not implemented. Is there a reason than lack of time for this? Are there any major difficulties? Cheers, Gaël

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NumPy-Discussion November 2008