al at beshenov.ru
Thu Mar 20 04:57:15 CDT 2008
On Thursday 20 March 2008 07:49, Robert Dodier wrote:
>> In my opinion, vect.mac approach is better. Anyway, this behavior could
>> be controlled by some flag.
> I think the multitude of flags makes it difficult for the user to
> understand what is going on, since the same code can have a
> different effect depending on flags. So I am not in favor of
> introducing another flag.
vector package can leave noun forms by default and compute operators in given
coordinates by some function or if some flag is "true" (it should be "false"
> Another way to avoid the whole listarith problem is to represent
> vectors as objects distinct from lists, e.g. vector(1, 2, 3)
> instead of [1, 2, 3]. Actually I am in favor of that; conflating
> different kinds of objects for convenience leads to unexpected
> results (e.g. listarith problems with vectors).
Lists are OK. listarith does unexpected things only with atoms which are
"not nonscalarp(x)". So we should force user to "declare(x,nonscalar)" for
every atom x which is intended to be a vector:
(%i1) x . [1,2,3];
(%o1) x . [1, 2, 3]
(%i2) x * [1,2,3];
(%o2) [x, 2 x, 3 x]
(%i3) x + [1,2,3];
(%o3) [x + 1, x + 2, x + 3]
(%i5) x + [1,2,3];
(%o5) x + [1, 2, 3]
Alexey Beshenov <al at beshenov.ru>
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