Re: [ublas] Solving linear equations of the form Ax = b ?

From: Sohail Somani (s.somani_at_[hidden])
Date: 2006-04-13 16:45:14

Im sure it can, but perhaps the author assumed you knew whether or not
the matrix was singular (I tend not to assume this) 

> -----Original Message-----
> From: ublas-bounces_at_[hidden] 
> [mailto:ublas-bounces_at_[hidden]] On Behalf Of Manoj Rajagopalan
> Sent: Thursday, April 13, 2006 12:53 PM
> To: ublas mailing list
> Subject: Re: [ublas] Solving linear equations of the form Ax = b ?
> 
> I can confirm that this code will crash on singular matrices 
> :-) Can't 
> ublas be modified to throw an exception or return an error value like 
> INFO in the original FORTRAN version?
> 
> 
> Sohail Somani wrote:
> > Warning: I think the wiki says that this code will crash on 
> a singular
> > matrix. 
> > 
> > Just fyi. 
> > 
> > 
> >>-----Original Message-----
> >>From: ublas-bounces_at_[hidden] 
> >>[mailto:ublas-bounces_at_[hidden]] On Behalf Of Manoj 
> Rajagopalan
> >>Sent: Thursday, April 13, 2006 7:06 AM
> >>To: ublas mailing list
> >>Subject: Re: [ublas] Solving linear equations of the form Ax = b ?
> >>
> >>you can solve Ax=b using three lines of ublas code:
> >>
> >>permutation_matrix<> piv;
> >>lu_factorize(A, piv);
> >>lu_substitute(A, piv, x);
> >>
> >>Then x will contain the solution and A is overwritten with its LU 
> >>decomposition. i.e., the original values of A and x are 
> >>destroyed so the 
> >>above lines are actually the inplace_solve(A, x) for a dense, 
> >>generic A.
> >>
> >>BTW, I've come across this in many places - what does 
> >>"boilerplate code" 
> >>mean and why is it called so?
> >>
> >>cheers!
> >>Manoj
> >>
> >>
> >>
> >>John Maddock wrote:
> >>
> >>>I gather from a quick web search that ublas does have LUP 
> >>
> >>decomposition 
> >>
> >>>routines, however a grep of the docs failed to find any 
> >>
> >>mention of the 
> >>
> >>>routine in question, and how they should be used.
> >>>
> >>>So.... does anyone have the boiler plate code needed to 
> >>
> >>solve for x given 
> >>
> >>>matrix A and vector b ?
> >>>
> >>>Many thanks,
> >>>
> >>>John Maddock. 
> >>>
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> >>
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