# Ublas :

Subject: Re: [ublas] size1 and size2
From: Marco Guazzone (marco.guazzone_at_[hidden])
Date: 2009-09-14 03:47:49

On Mon, Sep 14, 2009 at 4:23 AM, er <erwann.rogard_at_[hidden]> wrote:
> Nasos Iliopoulos wrote:
>>
>> I have a problem with rows and cols like other people have with left and
>> right. I have to think which is which :).
>> Beyond that I  prefer size1 and size2 for the same reasons Curtis does,
>> but i don't see much of a problem providing overloads to them under the
>> umbrella of a utils.h header or something.
>> size<1> and size<2> would be my personal favourite (as Gunter proposed),
>> but I think it goes too much for the average user.
>>
>> Best
>> Nasos
>>
>
> size_major would be closer to the STL convention, and avoids a new
> convention (row) on top of another (major). However size1, size<1>, or
> perhaps size<0> all seem fine.
>

Hello!

I think it would be necessary to distinguish between the matrix
theoretical concept from implementation detail.
I'm not a mathematician so correct me if I'm wrong.
For what I know a matrix is defined in terms of rows and columns; for instance:
* From http://en.wikipedia.org/wiki/Matrix_%28mathematics%29
"A matrix with m rows and n columns is called an m-by-n matrix or m
× n matrix, while m and n are called its dimensions"

* From http://mathworld.wolfram.com/Matrix.html
"An mXn matrix consists of m rows and n columns, and the set of mXn
matrices with real coefficients is sometimes denoted R^(mXn)"

What is argued in the previous emails is about matrix orientation that
IMO is an implementation detail.
So, if I declare a ublas::matrix(m,n) what I expect is that this
matrix has m rows and n columns regardless its orientation

Note, this is what I expect. Maybe it is not the phylosophy under the uBlas lib.
Let me know in this case and I'll stop to stress ;))

Anyway, maybe we can keep the two concept separate. So for a matrix A(m,n):
A.num_rows() ==> m
A.num_cols() ==> n
A.size1() ==> m if row_major OR n if column_major
A.size2() ==> n if row_major OR m if column_major
At least this is how the choice made by MTL4 (actually it uses dim1
and dim2 in place of size1 and size2, respectively).

What do you think?

Cheers,

-- Marco