[Numpy-discussion] Two bugs in numpy 0.9.2 and a suggestion.

Paulo J. S. Silva pjssilva at ime.usp.br
Thu Jan 12 03:39:01 CST 2006


I have just installed numpy 0.9.2 in my system. Thanks for the good
work. I think I got two bugs:

1) In the numpy.linalg method the cholesky decomposition doesn't work
because the function triu is not available from numpy.core. If you add a
line "from numpy import triu" on the top of the linalg.py file (with the
other imports), it starts working.

2) If you try to instantiate a ndarray with weird parameters it can
segfault and abort the interpreter. For example try to do the following:

a = arange(10.)
b = ndarray(a)

Now the suggestion. What about adding a "transpose" property (in the
Python parlance) to ndarray objects? I would call it "t". The following
Python code explains what I mean:

from numpy import *
class Myndarray(ndarray):
    t = property(transpose, None, None)

If you add this 3 lines to a file, import the Myndarray class, and
create one of such arrays you will get transpose(a) by simply typing
a.t. This allow for the following type of code (which I prefer):

cost = dot(c.t, x)

instead of 

cost = dot(transpose(c), x)


cost = dot(c.transpose(), x)

Such a compact notation can be a blessing in code that needs lots of
transpose (like the BFGS formula for example).

If I knew more about writing C extensions for Python I would try to do
it myself, but I don't. Is it possible to define properties in a C


Paulo José da Silva e Silva 
Professor Assistente do Dep. de Ciência da Computação
(Assistant Professor of the Computer Science Dept.)
Universidade de São Paulo - Brazil

e-mail: rsilva at ime.usp.br           Web: http://www.ime.usp.br/~rsilva

Teoria é o que não entendemos o     (Theory is something we don't)
suficiente para chamar de prática.  (understand well enough to call

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