[Numpy-discussion] Question: why is this different?

meng at are.berkeley.edu meng at are.berkeley.edu
Mon Oct 17 14:12:23 CDT 2005


Hi there-

I have a question on how this difference arises when I run the following 
simple code on windows and Debian:
 >>> from numarray import *
 >>> a=reshape(arange(81.0), (9,9))+identity(9)
 >>> ca = matrixmultiply(transpose(a),a)
 >>> import numarray.linear_algebra as la
 >>> ica = la.inverse(ca)
 >>> ica.min()
-0.30951621414374736
 >>> ica.max()
0.8888918586585135

The above is the result in Debian and below is that in Windows:
 >>> ica.min()
-0.30951621414449404
 >>> ica.max()
0.88889185865875686

So, what caused this difference (both machines have python2.4 and numarray 
1.3.2)? The difference happens in the 10th/11th decimal point, which should 
be still in the floating point precision, right? This simple difference 
caused big differences in my later calculation.

Best,
Xiangyi






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