Mailman 3 September 2010 - NumPy-Discussion

Unexpected float96 precision loss
by Michael Gilbert 02 Sep '10

02 Sep '10

Hi, I've been using numpy's float96 class lately, and I've run into some strange precision errors. See example below: >>> import numpy >>> numpy.version.version '1.5.0' >>> sys.version '3.1.2 (release31-maint, Jul 8 2010, 01:16:48) \n[GCC 4.4.4]' >>> x = numpy.array( [0.01] , numpy.float32 ) >>> y = numpy.array( [0.0001] , numpy.float32 ) >>> x[0]*x[0] - y[0] 0.0 >>> x = numpy.array( [0.01] , numpy.float64 ) >>> y = numpy.array( [0.0001] , numpy.float64 ) >>> x[0]*x[0] - y[0] 0.0 >>> x = numpy.array( [0.01] , numpy.float96 ) >>> y = numpy.array( [0.0001] , numpy.float96 ) >>> x[0]*x[0] - y[0] -6.286572655403010329e-22 I would expect the float96 calculation to also produce 0.0 exactly as found in the float32 and float64 examples. Why isn't this the case? Slightly off-topic: why was the float128 class dropped? Thanks in advance for any thoughts/feedback, Mike

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Equivalent Matlab function
by Matthieu Brucher 02 Sep '10

02 Sep '10

Hi, I'm looking for a Numpy equivalent of convmtx (http://www.mathworks.in/access/helpdesk/help/toolbox/signal/convmtx.html). Is there something inside Numpy directly? or perhaps Scipy? Matthieu -- Information System Engineer, Ph.D. Blog: http://matt.eifelle.com LinkedIn: http://www.linkedin.com/in/matthieubrucher

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Array slices and number of dimensions
by Thomas Robitaille 01 Sep '10

01 Sep '10

Hi, I'm trying to extract sub-sections of a multidimensional array while keeping the number of dimensions the same. If I just select a specific element along a given direction, then the number of dimensions goes down by one: >>> import numpy as np >>> a = np.zeros((10,10,10)) >>> a.shape (10, 10, 10) >>> a[0,:,:].shape (10, 10) This makes sense to me. If I want to retain the initial number of dimensions, I can do >>> a[[0],:,:].shape (1, 10, 10) However, if I try and do this along two directions, I do get a reduction in the number of dimensions: >>> a[[0],:,[5]].shape (1, 10) I'm wondering if this is normal, or is a bug? In fact, I can get what I want by doing: >>> a[[0],:,:][:,:,[5]].shape (1, 10, 1) so I can get around the issue, but just wanted to check whether the issue with a[[0],:,[5]] is a bug? Thanks, Tom

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Developer Job Openings at Space Telescope Science Institute
by Perry Greenfield 01 Sep '10

01 Sep '10

We are advertising for two different positions at the Space Telescope Science Institute (located on the Johns Hopkins University Campus in Baltimore, Md). STScI is seeking Senior Systems Software Engineers to develop applications to calibrate and analyze data from the Hubble and the James Webb Space Telescopes. **************************************************************************** First position: Description The developer will work with other members of the Science Software Branch and instrument scientists to develop applications to calibrate and analyze data from the Hubble Space Telescope and its successor, the James Webb Space Telescope, as well as other astronomy-related projects. The individual will be developing open source applications primarily in Python and C, using open source tools developed at STScI, such as PyRAF and PyFITS, and elsewhere. Some projects may involve developing software applications or libraries as part of a team, or leading a team. Requirements Candidates should have experience writing applications to calibrate, reduce, and analyze scientific data, preferably astronomical data. A background in astronomy and experience with astronomical data reduction is highly desirable. Candidates should have experience writing large programs in a compiled language as well as experience with an interpreted language such as IDL, Matlab, or Python. Experience using array manipulations facilities such as are available in IDL, Matlab, numpy/numarray, or APL is a plus. Experience using software engineering tools such as debuggers, CVS or subversion, and bug trackers is strongly desired. Strong analytical, problem-solving, planning, and organizational skills are needed, and excellent written and verbal communication skills are essential. Prior experience in developing medium or large projects sufficient to demonstrate the specified knowledge, skills and abilities is required. Qualified candidates should possess a Bachelor's degree in a science- related field such as Physics, Astronomy, or Mathematics. A Master's or Ph.D degree is desirable. Substitution of additional relevant education or experience for the stated qualifications may be considered. Apply through the following link: https://www.ultirecruit.com/SPA1004/jobboard/JobDetails.aspx?__ID=*6D48E0EF… **************************************************************************** Second position: Description The developer will work with other members of the Science Software Branch to help in enhancing and maintaining our Python-based framework for developing astronomical data analysis and calibration applications. STScI has pioneered in the generation of tools for using Python for scientific analysis and programming through its development of PyRAF, numarray, PyFITS, and contributions to other Python Open Source projects. The individual being sought will help STScI maintain its leadership in this area by developing leading-edge capabilities by enhancing existing tools such as PyRAF and PyFITS, contributing to scipy, numpy, and matplotlib, and developing new libraries to meet the needs of future astronomical processing. Some projects may involve developing software tools as part of a team, or leading a team. Work will also require working with an external community on Open Source software projects. Requirements Candidates should be experienced with systems-level programming, preferably with C or C++ and familiar with variances in processor and operating system architectures (preferably Linux, OS X, and MS Windows) with regard to file systems, memory, data types and efficiency, as well as modern software development techniques including Object-Oriented design and programming. Experience with Python and writing C extensions for Python is highly desirable. A working knowledge of any of the following would be a plus: parsers, code generation, numerical techniques, image processing and data analysis, web and network protocols, or parallel processing. Experience using software engineering tools such as debuggers, version control systems (e.g., subversion), and bug trackers is strongly desired. Strong analytical, problem-solving, planning, and organizational skills are needed, and excellent written and verbal communication skills are essential. Prior experience in developing medium or large projects sufficient to demonstrate the specified knowledge, skills and abilities is required. Qualified candidates should possess a Bachelor's Degree in Computer Science, Physics, Math, or technically related field. Master's degree preferred. Substitution of additional relevant education or experience for the stated qualifications may be considered. Apply through the following link: https://www.ultirecruit.com/SPA1004/jobboard/JobDetails.aspx?__ID=*85D01A9E… **************************************************************************** STScI offers an excellent benefits package, tuition reimbursement, competitive salaries, and a stimulating work environment. Interested candidates are requested to complete an on-line application, attach a resume in the "Resume Upload Section." Please include job #10-0083 in the filename. Resumes received by October 15, 2010 will receive full consideration. Committed to the benefits of diversity, we strongly encourage qualified women and minority candidates to apply. EOE/AA/M/F/D/V.

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Parsing PyArrays
by Babak Ahmadi 01 Sep '10

01 Sep '10

Hi, I'm having a little Problem that might be trivial. I'm trying to use a nupmy array within a c++ method and having some trouble. The PyArray is not parsed correctly and PyArg_ParseTuple returns 0. Appreciate any help. #include "Python.h" #include <numpy/arrayobject.h> void fromMatrix(PyObject *args){ _import_array(); PyArrayObject* A; PyArrayObject* B; if (!PyArg_ParseTuple(args, "O!O!", &PyArray_Type,&A, &PyArray_Type,&B)) return; int m = PyArray_DIM(A,0); int n = PyArray_DIM(A,1); .... and so on.

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Where is the dev version of numpydoc?
by John Salvatier 01 Sep '10

01 Sep '10

Hello, I would like to update my numpydoc so it works with sphinx 1.0, but I am not sure where the dev version is; can someone point me in the right direction? John

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