RE: [Vxl-users] vnl_lsqr doesnt solve Ax=b

[Andrew F. <aw...@ro...>]

MATLAB will be fast for that matrix as it checks for 
symmetry (at the very least).

Try A(i,i) = 1; A(i,i+1) = -2; A(i,i+2) = 1;



> -----Original Message-----
> From: vxl...@li... 
> [mailto:vxl...@li...] On Behalf Of 
> do...@vi...
> Sent: 28 March 2002 10:44
> To: Vxl...@li...
> Subject: Re: [Vxl-users] vnl_lsqr doesnt solve Ax=b
> 
> 
> Well my feeling is that 2*n is enough. I get a good solution for
> n=10,000 for 20,000 iterations. But it takes very long. Do you think I
> could try using svd in my case to gain speed?
> 
> 
> > > whereas for 30 equations it goes banana (wrong solution):
> > > vnl_lsqr.cxx : The iteration limit ITNLIM was reached.
> > > vnl_lsqr.cxx : iterations             = 30
> >
> > Could you try changing the # iterations to 120 in this case?
> 
> 
> 60 already gave good results in my case.
> 
> *I DONT KNOW IF THIS DOESNT DEPEND ON THE MATRIX* I used pretty naive
> one:
> 
>   for (unsigned i=0; i<n; i++) {
> 	 A(i,i)         = i+1.0;
> 	 b(i)           = i+10.0;
>   }
> 
> so the solution can be check by head.
> 
> Domi
> 
> 
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