Re: [Help-gsl] How does this cycle https://github.com/ampl/gsl/blob/master/linalg/svd.c#L117 work?

[Marco Ippolito]

Hi Patrick,
thank you for the paper. I do actually proceed by comparing this paper and
the algorithms in "Matrix Computations fourth Edition", Golub and Loan with
the code in  https://github.com/ampl/gsl/blob/master/linalg/svd.c
<https://github.com/ampl/gsl/blob/master/linalg/svd.c#L117> *which should
be working*.
This is why the the gls code has to be fully understood, especially in its,
apparenty, odd implementation, like this strange cycle

Marco

2017-06-19 11:35 GMT+02:00 Patrick Alken <address@hidden>:

> I don't know the answer to your question, but its probably more helpful
> to take a look at the SVD algorithm description in Golub and Van Loan,
> on which the GSL code is probably based. Also its probably worthwhile to
> look at the original paper, which I found here:
>
> http://people.duke.edu/~hpgavin/SystemID/References/
> Golub+Reinsch-NM-1970.pdf
>
> There is a complete pseudo-code writeup given in section 4.
>
> Patrick
>
> On 06/16/2017 04:19 PM, Marco Ippolito wrote:
> > Hi all
> > I do not undderstand this while cycle :
> > https://github.com/ampl/gsl/blob/master/linalg/svd.c#L117
> >
> > It seems to me that the only time when b is decremented is here:
> > https://github.com/ampl/gsl/blob/master/linalg/svd.c#L123
> > so when fbm1 == 0.0 where fb1 is the value of f at index = b-1 :
> > https://github.com/ampl/gsl/blob/master/linalg/svd.c#L119
> >
> > Since I'm trying to write my own C++11 code based on GSL code, I would
> like
> > to understand how it can work.
> > Any ideas?
> >
> > Looking forward to your kind help.
> > Marco
>
>
>
>