Mailman 3 May 2006 - SciPy-User

Help required regding Eigenvectors
by Sudheer Phani March 14, 2022

March 14, 2022

Hello All, I have been encountering some strange problems with the calculation of eigen vectors using python. The problem is with the sign of the eigen vectors calculated. On Very few occasions the eigen vectors calculated using python have an opposite sign than the actual eigenvectors, though the magnitude is correct. Can any one of you plz help me in this regard and suggest me some solution if you have encoutered similar problems . Any help in this regd is appreciated Thanks in Advace regds Sudheer

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3D plotting
by Robert Cimrman Sept. 10, 2009

Sept. 10, 2009

Hi, I need to do some simple 3D plots, so I tried the two Cookbook recipes (xplt, mplot3d) and failed: * xplt: does not work when using a custom installation directory such as python setup.py install --root=/home/share/software apparently the gistdata directory path is wrong: gist.error: failed to create drawing -- Gist work.gs style sheet missing * mplot3d: does not work with my version of matplotlib (0.80). I have made the changes mentioned in the Cookbook to no avail. (Axes.__init__() args apparently changed, as well as some other matplotlib object attributes) Any ideas? mplot3d looks great, I would really like to use it! thanks, r.

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Sparse matrix usage, documentation.
by Neilen Marais July 7, 2006

July 7, 2006

Hi The documentation for the sparse matrix classes seem to be, well, sparse. Does documentation exist somewhere I'm missing, or is it simply to early in the development process for much documentation to be around? I may be able to commit some once I understand what's going on though :) Right now I'd like to know more about the different sparse matrix types. I understand pretty much what coo, csc, and csr matrices are. From the docstrings I can more or less figure out what dok_matrix is, but what are dod_matrix and lnk_matrix? For naive matrix filling (i.e. if you don't know the sparsity pattern before hand) dok_matrix seems to be the best choice. Are there other useful formats for this purpose? When solving the matrix using iterative techniques, would it be better to convert it to one of the other sparse formats first, or can the dok matrix be solved efficiently itself? Thanks Neilen -- you know its kind of tragic we live in the new world but we've lost the magic -- Battery 9 (www.battery9.co.za)

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Re: [SciPy-user] SciPy-user Digest, Vol 33, Issue 41
by R. Padraic Springuel June 1, 2006

June 1, 2006

I've already created something similar. http://www.umit.maine.edu/~r.springuel/000CCFE8-80000018/S1EFF9C16.-1/scima… It contains all the constants defined in the 77th edition of the CRC handbook in SI units (with a few exceptions). Constants are referenced both by long name (such as speed_of_light_in_vacuum) and their common abbreviation (c). Uncertainties are not included. The code is fairly well commented. -- R. Padraic Springuel Teaching Assistant Department of Physics and Astronomy University of Maine Bennett 214 Office Hours: Wednesday 3:00 - 4:00 pm; Friday 12:30 - 1:30 pm

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Ipython Startup
by nicholas cunliffe May 31, 2006

May 31, 2006

Hi I have installed IPyhon but cannot get it to start. When I invoke it a dos type window flashes up for a fraction of a second and then disapears. Does anyone have any suggestions? Python 2.4(207) IPython 0.6.15 Thanks N

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Re: [SciPy-user] module with physical constants
by O'Keefe, Michael May 31, 2006

May 31, 2006

I'm happy to see a move towards a physical constants and units package. Just thought I'd mention that another source that may be worth noting/referencing for ideas is the SIUnits module in the Modelica language: http://www.dynasim.se/ModelicaStandardLibrary/help/Modelica_SIunits.html#Mo… This is not python (in fact it's the Modelica language) but I think one can get some ideas for a python implementation from here. -Michael FYI. For those who want to reference, Modelica is at http://www.modelica.org -----Original Message----- From: scipy-user-bounces(a)scipy.net [mailto:scipy-user-bounces@scipy.net] On Behalf Of Travis N. Vaught Sent: Wednesday, May 31, 2006 8:58 To: SciPy Users List Subject: Re: [SciPy-user] module with physical constants Darren Dale wrote: > On Tuesday 30 May 2006 11:24 pm, Robert Kern wrote: > >> Travis Oliphant wrote: >> >>> weg werp wrote: >>> >>>> http://physics.nist.gov/cuu/Constants/ >>>> >>>> combined with some other constans like conversion factors between >>>> imperial and SI, lightyears, arcminutes etc. If everything is defined >>>> in SI units, you could do tricks like >>>> >>>> >>> >from constants import * >>> >>>> speed = 23454 * parsec / week # in m/s >>>> print 'your are going',speed/Mach,'times the speed of sound.' >>>> p = 18 * torr # in Pascal >>>> print 'the pressure is', p/atm, 'atmosphere or', p/psi, 'pounds per >>>> square inch'. >>>> >>> I like this style for doing unit conversions. I think keeping it >>> simple as a module of float constants is a great idea. >>> >> I would prefer that the underlying database of constants and units is that >> dictionary full of "ugly" names provided by Chuck so long ago. Among other >> things, it's programmatically accessible. A more convenient set of variable >> names can be glommed into a neighboring module that indexes into that >> dictionary. >> >> And yes, I want the full set of CODATA Recommended Values. >> >> I do have reservations about such a thing becoming *the* scipy module for >> doing unit conversions, though. >> > > What if the constants were defined in SI, but let each constant derive from a > class or classes with methods that take care of conversion to other unit > systems. I was thinking of using gettable, but not settable, object > properties like si, cgs, emperial... Maybe the module could even be designed > such that the desired unit system is set as the default at module load time, > so the user could do "c=lightspeed" instead of "c=lightspeed.cgs". This would > still be compatible with further unit conversions, like "lightspeed/week". > > I remember trying to do conversion between electromagnetic units and SI, which > I was never quite able to wrap my head around. It would really be nice to > have unit conversion built in somehow. > > Darren > > It seems like the real thrust of this thread is to have a simple constants module(s), but the conversation has ballooned a bit into the (valid) need for a full-blown unit package. This has been don before in the Unum module mentioned as well as a units package (based on a fork of Michael Aivazis's units package) included with the Enthought Tool Suite ('ETS' -- which some folks may be surprised they already have installed if they're using a recent version of the Python Enthought Edition distro). The ETS units package could still use some work in it's handling of "unit families" (or 'measure-of') but it does provide all the functionality you're mentioning (conversion, unit systems). It's probably easier to show than to explain: C:\>python Python 2.3.5 - Enthought Edition 0.9.7 (#62, May 11 2005, 20:02:58) [MSC v.1200 32 bit (Intel)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> from enthought.units.mass import * >>> from enthought.units.energy import * >>> from enthought.units.speed import * >>> mass = 1*kg >>> mass 1.0*kg >>> C = 299792458.0*meters_per_second # no constants included, (still guessing the right numbers) >>> C 299792458.0*m*s**-1 >>> E = mass*C**2 >>> E 89875517873681760.0*m**2*kg*s**-2 >>> joule # check to see if this is in Joules 1.0*m**2*kg*s**-2 These are obviously objects, though... >>> E.__class__ <class 'enthought.units.unit.unit'> ...so you don't get the lightweight notion of simple floats assigned to symbols in the namespace as Travis O. was saying. Which begs the question of whether you really want the namespace mangling which comes from a "from constants import *" If I understand it right, I think I like Robert's dictionary idea. Travis _______________________________________________ SciPy-user mailing list SciPy-user(a)scipy.net http://www.scipy.net/mailman/listinfo/scipy-user

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module with physical constants
by weg werp May 31, 2006

May 31, 2006

Hi group, I have a background in physics and I find myself repeatedly defining things like c=3e8 when I am lazy, or c=299792458 when I need the accuracy. It would be nice to do just 'from constants import c' and get the correct value without having to grab for some handbook of physics and risk a typo. I made a small list of things I use myself. I am willing to spend some time extending the list with some more commonly used values, but only if people here find it useful for inclusion in Scipy. An obvious start would be the 'frequently used constants' table from http://physics.nist.gov/cuu/Constants/ combined with some other constans like conversion factors between imperial and SI, lightyears, arcminutes etc. If everything is defined in SI units, you could do tricks like from constants import * speed = 23454 * parsec / week # in m/s print 'your are going',speed/Mach,'times the speed of sound.' p = 18 * torr # in Pascal print 'the pressure is', p/atm, 'atmosphere or', p/psi, 'pounds per square inch'. I did some googling, and it appears that someone has done this before: http://old.scipy.org/mailinglists/mailman?fn=scipy-dev/2002-October/001259.… The problem I have with that version is that I don't like the format (it is in a dict with ugly names) and that he imports the complete CODATA set, which is too much (I think the number of users for the 'shielded helion gyromagn. ratio over 2 pi' is limited). The use case for the various uncertainties in the constants is also limited I guess. I am not planning to include the complete periodic system, just the basic stuff. I remember one language (pascal?) that had a scientific data type, which kept track of all the SI units during calculations. I have never seen anybody using such a thing, so that is probably overkill too. A simple module with some float constants is probably enough. Any interest for this or am I wasting my time? Cheers, Bas

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Re: [SciPy-user] module with physical constants
by morovia May 31, 2006

May 31, 2006

Hello, May be interconversion between various physical units also desirable. e.g mass.changeto('kg')- yields in kilogram. Also my wish list are the chemical constants and periodic table. Thanks Morovia.

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scipy not easy_install-able
by Stian Soiland May 30, 2006

May 30, 2006

I tried, naively perhaps, to install scipy using easy_install[1]: : stain@sandra ~;sudo easy_install scipy Searching for scipy Reading http://www.python.org/pypi/scipy/ Reading http://www.scipy.org Reading http://new.scipy.org/Wiki/Download Best match: scipy 0.4.9 Downloading http://193.190.198.97/sourceforge/scipy/scipy-0.4.9.tar.gz Processing scipy-0.4.9.tar.gz Running scipy-0.4.9/setup.py -q bdist_egg --dist-dir /tmp/easy_install-Mjgb6D/scipy-0.4.9/egg-dist-tmp-sgJBNS SandboxViolation: open('/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/site-packages/numpy/testing/info.py', 'U') {} The package setup script has attempted to modify files on your system that are not within the EasyInstall build area, and has been aborted. This package cannot be safely installed by EasyInstall, and may not support alternate installation locations even if you run its setup script by hand. Please inform the package's author and the EasyInstall maintainers to find out if a fix or workaround is available. (..) File "setup.py", line 50, in ? File "setup.py", line 23, in setup_package File "/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/site-packages/numpy/__init__.py", line 42, in ? __doc__ += pkgload.get_pkgdocs() File "/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/site-packages/numpy/_import_tools.py", line 319, in get_pkgdocs retstr = self._format_titles(titles) +\ File "/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/site-packages/numpy/_import_tools.py", line 282, in _format_titles max_length = max(lengths) ValueError: max() arg is an empty sequence [1] http://peak.telecommunity.com/DevCenter/EasyInstall I don't know quite why this things happens, if it is scipy, numpy or easy_install's fault. It would be nice to install via easy_install instead of doing it manually. I am afraid I don't have time to look further into the matters right now.. I am on: OS X 10.4, Python 2.4.1, numpy 0.9.4 -- Stian Søiland Any society that would give up a little Manchester, UK liberty to gain a little security will http://soiland.no/ deserve neither and lose both. [Franklin] =/\=

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Re: [SciPy-user] Looking for triangulator/interpolator
by Travis E. Oliphant May 28, 2006

May 28, 2006

Grant Edwards wrote: > On 2006-05-27, Travis E. Oliphant <oliphant.travis(a)ieee.org> wrote: > >> Not that you made a bad choice. I do wonder, how much of your >> difficulty was with the interface to the underlying fitpack >> routines. > > I've no idea. I had never done anything with splines before, > so it's quite possible I just wasn't doing things right. I > never got it to work at all for non-gridded data (which is what > I needed). Since it wasn't stable even for gridded data, I > more or less gave up. > >> The interface is pretty involved as there are lots of >> parameter choices to the underlying routine. It's very >> possible the interface is broken in some strange way. > > I took a look at underlying Fortran code, but that made my > dizzy. Just to finish this thread, I should mention I spent some time yesterday looking into the details of the underlying surfit fucntion used by bisplrep. It appears to have difficulties when s=0 is used. It seems to be geared toward smoothing applications where you are trying to fit "noisy" scattered data to a smooth function. There are many warnings about choosing s to be too low. Thus, trying to use bisplrep for interpolation (instead of data smoothing) is probably going to be difficult with bisplrep. We still need a good N-d re-gridding algorithm in SciPy. -Travis

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