Re: Larger matrices

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Fri, 08 Aug 2008 16:11:57 +0200, Georg Bauhaus wrote:

> Dmitry A. Kazakov schrieb:
>> On Fri, 08 Aug 2008 13:35:04 +0200, Georg Bauhaus wrote:
> 
>>> Ada is a systems programming language. 
> 
>> What?! Ada is a universal purpose language.
> 
> Assembly language is universal,

It is Turing complete.

> too, as are Lisp and Prolog with FFI,
> and so on.

They are not. Lisp is a list-oriented language, Prolog is a logical
inference language.

> This notion of "purpose" is not very specific.
> Let me put is this way: Ada has to be especially good at
> systems programming, hence it has to be fairly low level.

Wrong. Where that follows from? Systems programming need not to be
low-level. It has to have abstractions close to ones typical for "systems."
There is no obvious connection between these. For example, Ada offers the
notion of protected action in order represent a systems-domain specific
concept of interrupt. It is a fairly high-level abstraction.

>> But an efficient or hardware-close implementation was certainly not the
>> concern of the Ada.Numerics.Generic_Real_Arrays design. Otherwise it would
>> not use functions at all.
> 
> What hardware?

Vector processors.

> Assume data flow hardware, and assume a way
> to put the function result in the input box of the next processing unit.
> What now?

Nothing, Ada.Numerics.Generic_Real_Arrays was not designed in order to
support this hardware. Which is the point. Ada is not low-level, and its
design goals are not focused solely on efficiency, but on usability,
portability and maintainability.

> I don't see how prototyping a hypertext graph algorithm
> requires a maximally efficient implementation of matrix
> computations.

Because of the problem size. Incidence matrices grow as O(n**2), i.e.
extremely fast.

> A production system may require increased
> efficiency. At that stage you have to pay attention to
> the tiny bits, possibly redesigning the algorithm.

So, what was prototyped then? Numerics is all about algorithms. Changing
matrix representation has a huge impact on the implementation of the
operations. Technically it means that you have to re-write everything.

This BTW is exactly the problem OP has. He has "prototyped" the thing using
Ada.Numerics.Generic_Real_Arrays. Now, he faces the problem that the
prototype does not scale due to stack overflow. The consequence is a need
in full redesign. Ergo, prototyping was time wasting.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de