Dear GAP Forum,
On 4 Feb 2013, at 11:38, Denise Torrão <denisetor...@hotmail.com> wrote:
>
> Hello, my name is Denise and I'm starting to work in GAP. I'm trying to
> compute a simple program, but I'm with some dificulty, because I implement a
> cycle for, and my values of the list change. The program is the following:
> algoritmo14:=function(p,D,c)
> local soma, soma2, aux, aux3,i,A,x;
> A:=[];A[1]:=[];x:=[];
> for j in [1..p-1] do A[1][j]:=0;od;A[1][p]:=c;
>
> for i in [1..p-1] do x[i]:=0;od;x[p]:=c;
> i:=p-1;
> soma:=0;
> while (i>0) do for aux in [i+1..p] do
> soma:=soma+D[aux]*x[aux]; od; if (soma >= D[i]) then
> x[i]:=x[i]+1; x[p]:=soma-D[i];
> for aux3 in [i+1..p-1] do x[aux3]:=0;
> od;Print("A1-> ",A,"\n");
> Add(A,x);Print("A2-> ",A,"\n"); i:=p-1; else
> i:=i-1; fi; soma:=0;od;
>
> return A;end;
> My problem is with the list A, that changes, and in the final all it's
> elements (except for the first one) are equal. Can someone help me? I guess
> is something very trivial, but as I said before, I'm taking my first steps
> with GAP, so I still have a lot of dificulties with this program.
> Very very thanks,
> Denise Torrão
I think the problem is the statement "Add(A,x)". This DOES NOT make a copy of x.
A simple example is
gap> l := [1];
[ 1 ]
gap> m := [];
[ ]
gap> Add(m,l);
gap> l[1] := 2;
2
gap> m;
[ [ 2 ] ]
gap>
Here m[1] and l are THE SAME list and changes to that list can be seen through
both routes. What you probably want is
Add(A, ShallowCopy(x));
which does make a copy.
Steve
_______________________________________________
Forum mailing list
Forum@mail.gap-system.org
http://mail.gap-system.org/mailman/listinfo/forum
