Mailman 3 November 2006 - NumPy-Discussion

Installing CVXOPT
by amit soni Nov. 25, 2006

Nov. 25, 2006

hi, how can I install and start using CVXOPT. I have python 2.5 version installed. what else do i need to download and install for CVXOPT. thanks amit ____________________________________________________________________________________ Want to start your own business? Learn how on Yahoo! Small Business. http://smallbusiness.yahoo.com/r-index

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A reimplementation of MaskedArray
by Pierre GM Nov. 23, 2006

Nov. 23, 2006

Folks, I just posted on the scipy/developers zone wiki (http://projects.scipy.org/scipy/numpy/wiki/MaskedArray) a reimplementation of the masked_array mopdule, motivated by some problems I ran into while subclassing MaskedArray. The main differences with the initial numpy.core.ma package are that MaskedArray is now a subclass of ndarray and that the _data section can now be any subclass of ndarray (well, it should work in most cases, some tweaking might required here and there). Apart from a couple of issues listed below, the behavior of the new MaskedArray class reproduces the old one. It is quite likely to be significantly slower, though: I was more interested in a clear organization than in performance, so I tended to use wrappers liberally. I'm sure we can improve that rather easily. The new module, along with a test suite and some utilities, are available here: http://projects.scipy.org/scipy/numpy/attachment/wiki/MaskedArray/maskedarr… http://projects.scipy.org/scipy/numpy/attachment/wiki/MaskedArray/masked_te… http://projects.scipy.org/scipy/numpy/attachment/wiki/MaskedArray/test_mask… Please note that it's still a work in progress (even if it seems to work quite OK when I use it). Suggestions, comments, improvements and general feedback are more than welcome ! ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642

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numpy.random.shuffle
by Robert Nov. 22, 2006

Nov. 22, 2006

is this an error when shuffle doubles&looses items on a 2-d array? : >>> r=arange(20) >>> rr=ziparrays(r,r) #numpy.vstack(*args).transpose() >>> rr array([[ 0, 0], [ 1, 1], [ 2, 2], [ 3, 3], [ 4, 4], [ 5, 5], [ 6, 6], [ 7, 7], [ 8, 8], [ 9, 9], [10, 10], [11, 11], [12, 12], [13, 13], [14, 14], [15, 15], [16, 16], [17, 17], [18, 18], [19, 19]]) >>> numpy.random.shuffle(rr) >>> rr array([[ 0, 0], [ 0, 0], [ 2, 2], [ 2, 2], [ 3, 3], [ 3, 3], [ 5, 5], [ 2, 2], [ 0, 0], [ 8, 8], [10, 10], [ 1, 1], [10, 10], [11, 11], [12, 12], [ 2, 2], [10, 10], [15, 15], [ 6, 6], [16, 16]]) >>> on 1-d arrays it seems to be consistent as expected: >>> numpy.random.shuffle(r) >>> r array([ 6, 1, 3, 17, 0, 11, 15, 7, 14, 10, 9, 2, 8, 12, 5, 4, 19, 16, 13, 18]) >>> Robert

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Numpy without BLAS, LAPACK
by vallis.35530053＠bloglines.com Nov. 22, 2006

Nov. 22, 2006

(Reposting to numpy-discussion(a)scipy.org instead of the SourceForge list.) It is my understanding that Numpy has "lite" versions of BLAS and LAPACK that it will use if it cannot find system libraries. Is it possible to FORCE it to use the lite versions rather than existing system libraries? (Where I come from: I'm trying to install numpy in a local directory on a Beowulf cluster, which has local BLAS and LAPACK that the numpy setup finds; however, these libraries are missing some functions, so "import numpy" fails at numpy.linalg. The fact is that I don't need numpy.linalg at all, so I'd be very happy with the lite libraries, rather than going to the trouble of recompiling BLAS and LAPACK or ATLAS, etc.) Michele

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approx. replacement for scipy.special.betainc ?
by Robert Nov. 22, 2006

Nov. 22, 2006

for the computation of a p_value I need the betainc function, which draws the big _cephes module into a (numpy-only) app - the only reason for this import. I need it just for the computation of a p-value like: p_value = scipy.special.betainc(0.5*nf, 0.5, nf/(nf+t_value*t_value)) Is there a simple (python-only) replacement func for betainc ? Robert

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How to deal with NAN and co in C extension to numpy/scipy ?
by David Cournapeau Nov. 22, 2006

Nov. 22, 2006

Hi, I am about to release some code to compute LPC coefficients (Auto regressive modeling, using Levinson Durbin algorithm for autocorrelation matrix inversion), and I was wondering how to handle cases of divide by 0, or values really near 0. I understand this is a complex issue, and I admittedly have no knowledge about it except some generalities; there are versions of Levinson Durbin which handles bad condition numbers (for people not familiar with LPC coding, levinson durbin is a recursive algorithm to inverse a symmetric Toeplitz matrix; the complexity becomes O(N^2) instead of O(N^3)); but they are overkill for LPC coding, I think. The options I see are: - I don't care :) - Detecting values near zero, finish the computation anyway in C, and returns an error code to python, which would emit a warning. - Detecting values near zero, returns an error code which would results in a python exception ? In this latter cases, is it ok to returns to python arrays the values from the C function ? In matlab, for bad cases, it just returns NAN; is this appropriate ? How should I do it ? cheers, David

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scipy Windows binary compatible recent numpy 1.0 ?
by Robert Nov. 22, 2006

Nov. 22, 2006

Since some months now the latest scipy (0.5.1) binary (for Windows) is not compatible with current numpy (1.0) - obviously because of a C-library mismatch. Does somebody have a compatible binary - or when is the next scipy (binary) planned? Robert

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Quadratic Optimization Problem
by amit soni Nov. 22, 2006

Nov. 22, 2006

Hi, I need to do a quadratic optimization problem in python where the constraints are quadratic and objective function is linear. Its a convex optimization problem. What are the possible choices to do this. Thanks Amit ____________________________________________________________________________________ Sponsored Link Rates near 39yr lows. $420,000 Loan for $1399/mo. Calcuate new payment. www.LowerMyBills.com/lre

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Numpy Documentation
by Colin J. Williams Nov. 21, 2006

Nov. 21, 2006

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fiddling the strides of an array
by A. M. Archibald Nov. 21, 2006

Nov. 21, 2006

Hi, I have a function that would like to be able to take an array, look at its 'strides' and 'shape' tuples, and fabricate another array that is similar to the first but has the adjusted values. For a simple example: def fiddle(a): strides = list(a.strides) strides[0]*=2 shape = list(a.shape) shape[0]//=2 return N.ndarray.__new__(N.ndarray, strides=strides, shape=shape, buffer=a, dtype=a.dtype) Unfortunately, this has a few problems. * It always makes ndarrays, even if the original was some subtype. (not a big deal for me, but still a bit annoying) * It fails unnecessarily if the array is not "contiguous": for example, fiddle(N.zeros((2,2,2,2)).swapaxes(0,2)) fails, saying "expected a single-segment buffer object". This second problem is my real problem. Is there a way I can tell numpy "no really, I know what I'm doing with these strides, use the same underlying memory as this array"? (Of course I can flatten the array, but that will copy it unnecessarily.) Thanks, A. M. Archibald

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