Mailman 3 February 2005 - 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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lognormal distribution
by Stephen Walton March 7, 2005

March 7, 2005

An application question for a change: I need to produce pseudorandom numbers drawn from a lognormal distribution (see http://www.itl.nist.gov/div898/handbook/eda/section3/eda3669.htm). Does anyone have existing code for this in Numeric or numarray?

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ANN: PyQwt3D-0.1 released
by Gerard Vermeulen Feb. 27, 2005

Feb. 27, 2005

What is PyQwt3D? - it is a set of Python bindings for the QwtPlot3D C++ class library which extends the Qt framework with widgets for 3D data visualization. PyQwt3D inherits the snappy feel from QwtPlot3D. The examples at http://pyqwt.sourceforge.net/pyqwt3d-examples.html show how easy it is to make a 3D plot and how to save a 3D plot to an image or an (E)PS/PDF file. - it requires and extends PyQt, a set of Python bindings for Qt. - it supports the use of PyQt, Qt, Qwt, the Numerical Python extensions (either Numeric, or numarray or both) and optionally SciPy in a GUI Python application or in an interactive Python session. - it runs on POSIX, MacOS/X and Windows platforms (practically any platform supported by Qt and Python). The home page of PyQwt3D is http://pyqwt.sourceforge.net. PyQwt3D-0.1 supports: 1. Python-2.4 downto -2.3. 2. PyQt-3.14 downto -3.12. 3. SIP-4.2 downto -4.0, but SIP-4.2 is recommended. PyQwt3D does *not* support SIP-3.x (I tried, but failed). 4. Qt-3.3.4 downto -2.3.0. 5. QwtPlot3D-0.2.4-beta. Have fun -- Gerard Vermeulen

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Partial Derivatives
by R. Padraic Springuel Feb. 26, 2005

Feb. 26, 2005

Is there a way to use the "derivative" function to take a partial derivative? What if one of the inputs is a list of numbers instead of a single number? Example: def y(x,p): return p[0] + p[1]*x + p[2]*x**2 I can get the derivative with respect to x fairly easily with the following: derivative(y, 3, args=([[0, 0, 1]]) where the numbers can be arbitrarily replaced. However I can't seem to get the derivative with respect to say p[0] or any other member of p. I keep getting a TypeError regarding the number of arguments for y. Any suggestions? -- R. Padraic Springuel

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SciPy.org and Enthought.com scheduled downtime today at ~12 CST
by Joe Cooper Feb. 24, 2005

Feb. 24, 2005

Hi all, Both SciPy.org and Enthought.com and all of the services that they host will be taken offline today at around noon CST. We are moving upstairs today and taking the servers with us. SBC willing, the servers will be out of service for no more than an hour or so. Anyway, if you're planning a check-in for lunchtime today, hold off a while, or get it in before then. ;-) Thanks!

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Eigenvalues for bandstructures problem...
by Paul Jefferson Feb. 24, 2005

Feb. 24, 2005

Hi, I have been using the linalg module in scipy (as well as the LinearAlgebra module in Numeric, and the Linear_Algebra module in numarray) to calculate the eigenvalues of a 4x4 hamiltonian matrix that calculates semiconductor bandstructures. A variable k is cycled through changing the elements of the matrix and the eigenvalues are obtained for each value of k. Each band is defined by one eigenvalue (0,1,2 or 3 in the returned array) for all k. On plotting the bands as a function of k. I noticed that the eigenvalues swap over at certain values of (+/-) k (best seen in the attached figure). I was wondering if anybody knew of this problem using the linalg package? (I don't have the same problem with octave (which I think also uses atlas)). If anyone can throw any light on this problem it would be much appreciated. Best Regards, Paul Jefferson.

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derivative
by Nils Wagner Feb. 23, 2005

Feb. 23, 2005

Hi all, Is it somehow possible to improve the accuracy of derivative ? A small example is attached. from scipy import * def func(x): return exp(2*x) for i in arange(1,6): print i,' derivative of exp(2*x) at x=0',derivative(func,0.0,0.01,i,order=7),'exact',2**i Any suggestion ? Nils

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ANN: PyQwt-4.2 released
by Gerard Vermeulen Feb. 23, 2005

Feb. 23, 2005

What is PyQwt? - it is a set of Python bindings for the Qwt C++ class library which extends the Qt framework with widgets for scientific, engineering and financial applications. It provides a widget to plot 2-dimensional data and various widgets to display and control bounded or unbounded floating point values. - it requires and extends PyQt, a set of Python bindings for Qt. - it supports the use of PyQt, Qt, Qwt, the Numerical Python extensions (either Numeric, or numarray or both) and optionally SciPy in a GUI Python application or in an interactive Python session. - it runs on POSIX, MacOS/X and Windows platforms (practically any platform supported by Qt and Python). The home page of PyQwt is http://pyqwt.sourceforge.net. PyQwt-4.2 is a maintenance release to keep up with the recent releases of PyQt-3.14 and its code generator SIP-4.2. PyQwt-4.2 supports: 1. Python-2.4 downto -2.1. 2. PyQt-3.14 downto -3.10. 3. SIP-4.2 downto -4.0, and SIP-3.11 downto -3.10. 4. Qt-3.3.4 downto -2.3.0. 5. Qwt-4.2.0. Have fun -- Gerard Vermeulen

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Pade approximants
by Nils Wagner Feb. 23, 2005

Feb. 23, 2005

Hi all, Has someone written a wrapper for the FORTRAN subroutine pade which is available through http://lib-www.lanl.gov/numerical/bookfpdf/f5-12.pdf It would be nice to have a function called pade in scipy :-) . Any comments or suggestions ? Nils

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Numeric Documentation
by Greg Novak Feb. 23, 2005

Feb. 23, 2005

Can someone please post the Numeric Documentation PDF file next to the HTML version here:http://numeric.scipy.org/. The HTML documetation renders illegibly in certain spots for me (text is placed on top of other text). I had been getting it from http://www.pfdubois.com/numpy/ but that site's been taken down. Thanks! Greg

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