Yes, this is a bug, set_partitions is not returning correctly
simplified sets -- could you please report it?
In the meantime, as a workaround, you can simplify the results of
set_partitions correctly by calling resimplify:
resimplify(expr):=expand(expr,1,1)$
is(listify(resimplify(set_partitions({1,2,3,4},3)))[3] = {{1},{3},{2,4}});
=> true
-s
On Fri, Mar 20, 2009 at 12:48 PM, Oliver Kullmann
<O.Kullmann at swansea.ac.uk> wrote:
> Hello,
>
> Using Maxima 5.17.1 with Ecl 8.12.0 I get
> the following bizarre behaviour:
>
> (%i1) listify(set_partitions({1,2,3,4},3));
> (%o1) [{{1},{2},{3,4}},{{1},{2,3},{4}},{{1},{3},{2,4}},{{1,2},{3},{4}},{{1,3},{2},{4}},
> ? ? ? {{1,4},{2},{3}}]
> (%i2) listify(set_partitions({1,2,3,4},3))[3];
> (%o2) {{1},{3},{2,4}}
> (%i3) is(listify(set_partitions({1,2,3,4},3))[3] = {{1},{3},{2,4}});
> (%o3) false
>
> There is clearly a bug here. It seems to me that the villain is set_partitions
> which doesn't seem to produce "good sets".
>
> Oliver
>
> P.S. It's not just the equality test not working, but e.g.
> (%i4) intersection(listify(set_partitions({1,2,3,4},3))[3], {{2},{2,1},{2,3},{2,4}});
> (%o4) {}
> (%i5) intersection({{1},{3},{2,4}}, {{2},{2,1},{2,3},{2,4}});
> (%o5) {{2,4}}
>
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