Re: [ublas] [bindings] LAPACK ?GESVD and minimum workspace size

Subject: Re: [ublas] [bindings] LAPACK ?GESVD and minimum workspace size
From: Rutger ter Borg (rutger_at_[hidden])
Date: 2011-04-07 06:52:37

On 04/07/2011 11:59 AM, sguazt wrote:

> I've tried to follow each path. I've end up with the following cases:
>
> --- [code] ---
> m = ...; // # rows of A
> n = ...; // # columns of A
> sz = 0; // will hold the min work size
> /* k = ::std::min(m,n); */
> if (m>= n /*&&  k>  0 */) {
>    if (jobu == 'N') {
>      //sz = ::std::max(4*n, 5*n);
>      sz = 5*n;
>    } else {
>      sz = ::std::max(3*n+m,5*n);
>    }
> } else /* if (k>  0) */ {
>    if (jobvt == 'N') {
>      // sz = ::std::max(4*m, 5*m);
>      sz = 5*m;
>    } else {
>      sz = ::std::max(3*m+n,5*m);
>    }
> }
> return sz;
> --- [code] ---
>
> Do you agree?

Looks promising. Would this be about the same as

minmn = min( m, n );
if ( jobu=='N' || jobvt == 'N' ) {
   return 5 * minmn;
} else {
   return max( 3 * minmn + max(m,n), 5 * minmn );
}

?

Cheers,

Rutger