Re: [Help-gsl] comment and code differ in francis.c, line 560,561

[Patrick Alken]

I'm pretty confident that the code is correct, as the francis module has 
been tested extensively on lots of different matrices. I think the 
confusion is between C indexing starting at 0, and matrix notation using 
1 as the first row/column.

On 11/02/2014 04:04 PM, Kurt Alan Franke wrote:
> Hello all,
>
> My first post. I am looking at the francis.c file of gsl-1.16, lines 560.. and 
> found:
>
>            /* q = max(1, i - 1) */
>            q = (1 > ((int)i - 1)) ? 0 : (i - 1);
>
>            /* r = min(i + 3, N - 1) */
>            r = ((i + 3) < (N - 1)) ? (i + 3) : (N - 1);
>
> The first comment doesn’t appear to agree with the code below.
>
> i   q   max(1,i-1)
> 0  0  1 <--
> 1  0  1 <--
> 2  1  1
> 3  2  2
> …
>
> Is the comment wrong, or is there an error in the code? I assume the comment 
> must be wrong. (?)
> Does someone have the Golub book to check?
>
> Kind regards,
> Kurt