Vectors and matrices

[Bill Baxter]

On Wed, Apr 15, 2009 at 7:07 AM, Lars Kyllingstad
<public at kyllingen.nospamnet> wrote:
> I am writing a D library based some of the stuff in SLATEC, and I've come to
> a point where I need to decide on a way to manipulate vectors and matrices.
> To that end, I have some ideas and questions I would like comments on from
> the community.
>
> Ideally, I want to restrict the user as little as possible, so I'm writing
> heavily templated code in which one can use both library-defined
> vector/matrix types and built-in arrays (both static and dynamic). My
> reasons for this are:
>
>   a) Different problems may benefit from different types. Sparse matrices,
> dense matrices, triangular matrices, etc. can all be represented differently
> based on efficiency and/or memory requirements.
>
>   b) I hope that, at some point, my library will be of such a quality that
> it may be useful to others, and in that event I will release it.
> Interoperability with other libraries is therefore a goal for me, and a part
> of this is to let the user choose other vector/matrix types than the ones
> provided by me.
>
>   c) Often, for reasons of both efficiency and simplicity, it is desirable
> to use arrays directly.
>
> My first question goes to those among you who do a lot of linear algebra in
> D: Do you think supporting both library  types and arrays is worth the
> trouble? Or should I just go with one and be done with it?
>
>
> A user-defined matrix type would have opIndex(i,j) defined, and to retrieve
> elements one would write m[i,j]. However, the syntax for two-dimensional
> arrays is m[i][j], and this means I have to put a lot of static ifs around
> my code, in order to check the type every time I access a matrix. This leads
> me to my second question, which is a suggestion for a language change, so I
> expect a lot of resistance. :)
>
> Would it be problematic to define m[i,j,...] to be equivalent to
> m[i][j][...] for built-in arrays, so that arrays and user-defined types
> could be used interchangeably?
>
> (And, importantly, are there anyone but me who think they would benefit from
> this?)

How about just making a lightweight array-view class that provides
your interface, but manipulates an underlying m[] passed to the
constructor by the user?

Another point is that if you are willing to write code like
index(m,i,j) inside your lib instead of m[i,j], then you only need the
static conditional inside the index() function.

--bb