[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Axiom-developer] How to enumerate a product of lists (or integer se

From: Francois Maltey
Subject: Re: [Axiom-developer] How to enumerate a product of lists (or integer sets)
Date: 15 Oct 2007 16:53:32 +0200
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.4

Many thanks dear Martin !

> L := concat [concat [concat [[[a,b,c,d] _
>                               for a in 1..9] _
>                              for b in 1..9] _
>                      for c in 1..9] _
>              for d in 1..9]
> and then loop over them:
> [eval(matrix [[a,b,15-a-b],[c,d,15-c-d],[15-a-c,15-b-d,15-a-d]], [a,b,c,d], 
>                 l) for l in L]

I ignore this way. It's better than this too long command line map :
map (l +-> matrix [[l.1,l.2,15-l.1-l.2],[...],[...]], L)

In mupad there is the short-cut
map ([a,b,c,d] -> matrix [[a,b,15-a-b],[c,d,15-c-d],[15-a-c,15-b-d,15-a-d]], L)

Is there no way to find it in axiom ?

The eval seems quite different : 
the map doesn't create any symbolic matrix 
but the eval create symbolic matrices. Am I right ?

> > a train of for creates only one zip-list.
> Yes, and that's something very useful! For example
> [f(l, i) for l in L for i in 1..]
> is in my opinion much better to read then [f(L.i, i) for i in 1..#L]
> and [f(l) for l in L for i in 1..4] for the four first.
It's right ! train of for are useful.

But I take note that exercices for my students use a lot 
of cartesian products with $...$... and very view train of for as above.

I don't suggest a where operator [f(i,j) for i in 1..10 where j in L] 
for cartesian product ;-)


reply via email to

[Prev in Thread] Current Thread [Next in Thread]