Re: [ublas] [bindings] lapack::lange: where is the computed norm?

Subject: Re: [ublas] [bindings] lapack::lange: where is the computed norm?
From: Marco Guazzone (marco.guazzone_at_[hidden])
Date: 2010-07-23 02:03:31

On Thu, Jul 22, 2010 at 11:15 PM, Rutger ter Borg <rutger_at_[hidden]> wrote:
> Marco Guazzone wrote:
>
>> Hi,
>>
>> According to LAPACK the ?LANGE function should return the computed norm.
>>
>> For instance, see:
>> http://www.netlib.org/lapack/explore-html/a00725_source.html
>>
>> However, in lapack::lange I'm not able to find neither a return value
>> nor an output parameter representing that norm.
>>
>> Can you help me?
>>
>> Thank you very much!!
>>
>> Best,
>>
>> -- Marco Guazzone
>
> Looks like a LAPACK function that returns stuff, and doesn't have an INFO
> parameter. I.e., it looks more like a BLAS function than like LAPACK
> function. Perhaps there's more in auxiliary that behaves like this?
>

Hi,

In auxiliary, there are a family of ?LAN?? functions
  http://www.netlib.org/lapack/lug/node144.html

used for computing the norm of a matrix.
These functions differ from the type of matrix they work with.
For instance, ?LANGE works with general matrices, while ?LANGB work
with general banded matrices and ?LANHB works with Hermitian banded
matrices.
It appears that all these functions are FORTRAN FUNCTION returning some value.
In bindings, it seems they are implemented as FORTRAN SUBROUTINE
(i.e., returns a std::ptrdiff_t instead of the value computed by the
function).

Cheers,

-- Marco