[SciPy-user] Bug in inverse matrixcalculation for "scipy_core-0.8.4.win32-py2.3.exe"

Randewijk P-J <pjrandew@sun.ac.za> pjrandew at sun.ac.za
Wed Dec 14 09:13:07 CST 2005


Now that you metion it... "sometimes" the inverse of some of my
supposedly singular matrixes has "very large" values, because the
determinant is actually not zero, but a "very small" value... e.g.

>>> linalg.det(m)
-1.5717747464951435e-006
>>> 



> -----Original Message-----
> From: scipy-user-bounces at scipy.net 
> [mailto:scipy-user-bounces at scipy.net] On Behalf Of Nils Wagner
> Sent: 14 December 2005 17:01
> To: SciPy Users List
> Subject: Re: [SciPy-user] Bug in inverse matrixcalculation 
> for "scipy_core-0.8.4.win32-py2.3.exe"
> 
> 
> Frank wrote:
> >"On this note.  Is there a way of determining before hand in 
> scipy if a 
> >matrix is singular, say by calculating its rank, e.g.:"
> >
> >if det(matrix) = 0, then the matrix is singular
> >
> >_______________________________________________
> >SciPy-user mailing list
> >SciPy-user at scipy.net http://www.scipy.net/mailman/listinfo/scipy-user
> >  
> This is not very reliable when using floating point 
> operations. See the book by Carl D. Meyer "Matrix analysis 
> and applied linear algebra" SIAM 2000 especially chapter 6 p. 
> 466 Example 6.1.2
> 
> Nils
> 
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> SciPy-user at scipy.net http://www.scipy.net/mailman/listinfo/scipy-user
> 



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