On Wed, 15 Apr 2009 10:07:38 -0400, Lars Kyllingstad
<pub...@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?
I'd say its worth the trouble.
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. :)
I consider m[i][j] to be a jagged array, which is logically different from
matrix types. (i.e. its not square, etc.)
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?
Actually, I'd prefer actual dense arrays over syntactic sugar for jagged
arrays.
(And, importantly, are there anyone but me who think they would benefit
from this?)
-Lars
Good numerics and linear algebra is always appreciated. To that end
there's a nice performance speedup in storing machine/byte strides instead
of logical/element strides. (See:
http://dobbscodetalk.com/index.php?option=com_content&task=view&id=502&Itemid=52
Also, my lab maintains a vector/numerics/robotics package that might be of
interest https://trac.lcsr.jhu.edu/cisst)
