The ABINIT Users Mailing List ( CLOSED )

["Allan, Douglas C Dr" <AllanDC@corning.com>]

Anundya, others,

I was about to suggest revised wording but I think the meaning of
"columnwise" is clearly spelled out in the text below where it occurs,
at least in version 5.5 whose online documentation I just checked.

Since the math and algorithm are spelled out there, I would not change
the text.
Sorry for confusion, but really the definition is very clearly spelled
out including the role of aprim.

If others disagree then someone may suggest revised wording.  I am
probably not an objective reader.

Best regards,
Doug

-----Original Message-----
From: Anindya Roy [mailto:royanin@gmail.com] 
Sent: Tuesday, October 21, 2008 2:59 PM
To: forum@abinit.org
Subject: Re: [abinit-forum] Definition of rprim

Hi Doug, Adam,

I indeed thought it's asking user to supply input in a specific
fashion, rather than expressing how the program is going to treat the
input supplied. But thank you all for taking time to clarify. Perhaps
one of you could come up with a sentence which would be unambiguous
even to a beginner :) Just a suggestion.

Thank you,
Anindya

On Tue, Oct 21, 2008 at 2:20 PM, Adam Sorini <asorini@gmail.com> wrote:
> On Mon, Oct 20, 2008 at 6:41 PM, Allan, Douglas C Dr
<AllanDC@corning.com>
> wrote:
>>
>> Adam,
>>
>>
>>
>> The word "columnwise" in this context means that the first 3 numbers
you
>> enter will fill out the first column and so forth.  You never enter
numbers
>> columnwise when you are reading files line by line, you just enter
numbers.
>>  It is not a misprint or typo.
>
> Hi Doug,
>
> Thanks for your clarification.
>
> I think the OP's point is that the doc is unclear. At the very least,
we can
> say that the doc was unclear to at least one user. ;)
>
> Just because a document contains no typos or misprints, that doesn't
mean
> that it is clearly written. As an example we could consider the very
first
> sentence of the description of rprim:
>
> "Give, in columnwise entry, the three dimensionless primitive
translations
> in real space."
>
> The correct interpretation (knowing that this phrase is a description
of
> rprim and not an order to the user) is that the (set of 9) rprim(i,j)
(they)
> give the primitive translation vectors as columns of the matrix rprim.
But,
> to an uninitiated person reading the doc the word "give" in the first
> sentence might sound like it is refering to "you". As in "[You] give
[via
> the input file in columns]... the three dimensionless primitive
translations
> in real space." This is the danger of having implied subjects in the
> documentation of one's computer program... ;)
>
> Oh well. Cheers,
>
> Adam
>
>>
>>
>> Also do not overlook the role of the length scale, which is defined
>> independently of rprim.  Rprim gets normalized after input so it
represents
>> directions that are of unit length.
>>
>>
>>
>> Cheers,
>>
>> Doug
>>
>>
>>
>> ________________________________
>>
>> From: Adam Sorini [mailto:asorini@gmail.com]
>> Sent: Monday, October 20, 2008 6:28 PM
>> To: forum@abinit.org
>> Subject: Re: [abinit-forum] Definition of rprim
>>
>>
>>
>> It's my understanding that
>>
>> rprim a b c
>>         d e f
>>         g h i
>>
>> mean that the primative vectors are R1 = (a,b,c), R2 = (d,e,f), R3 =
>> (g,h,i) and the matrix rprim(i,j) is
>> rprim(i,j) = Rj(i)
>>
>> So, I think that's what they mean by "columnwise". Just that the
first
>> index of array rprim(i,j) gives the components of the primative
lattice
>> vector. The use of the word "columnwise" in the first sentence of the
>> description of the basic input variable rprim then appears to be a
mistake
>> since we don't write the vectors in the input file "columnwise".
Cheers,
>>
>> Adam
>>
>> On Mon, Oct 20, 2008 at 2:17 PM, Anindya Roy <royanin@gmail.com>
wrote:
>>
>> Hi all,
>>
>> I'm having a little trouble to interpret the basic definition of
>> 'rprim' as stated in documentation of version 5.5.4 (and similar
>> ones): rprim is defined to be  "...in columnwise entry, the three
>> dimensionless primitive translations in real space."
>>
>> Later the example given for hexagonal lattice:
>>
>> "rprim  0.86602540378  0.5  0.0
>>      -0.86602540378  0.5  0.0
>>       0.0            0.0  1.0
>>
>> that can be avoided thanks to angdeg:
>>
>> angdeg 90 90 120
>> "
>>
>> It looks to me that new basis vectors are in row wise entry, rather
>> than column wise.
>>
>> So if we assume that the new vector R_1 is [rprim(11)\hat{x} +
>> rprim(12) \hat{y} + rprim(13) \hat{z}] , then it's internally
>> consistent how xred and xcart are converted among themselves. Am I
>> missing something obvious? Your thought will be greatly appreciated.
>>
>> Thanks,
>> Anindya Roy
>> Graduate student
>> Rutgers University, USA
>>
>>
>