#11576: make it possible to generate sequences of variables easily
---------------------------+------------------------------------------------
Reporter: kcrisman | Owner: burcin
Type: enhancement | Status: new
Priority: major | Milestone: sage-4.8
Component: symbolics | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
---------------------------+------------------------------------------------
Comment(by hivert):
Hi there,
As as said on sage-devel, I started to work on Burcin patch. My goal was
to be
able to index a variable by '''any''' Sage object (eg: integers, group
element, matrices...). So I extended a little Burcin patch. Now I'm faced
with
the problem that GiNaC indexed variable seems to have a not trivial
semantic
that I don't understand at all. Moreover I don't know how to debug Cython
/
C++ code so I'm quite stuck. Here is the problem I have.
To get it you should apply attachment:indexed_expression-experimental-
fh.patch
on a fresh Sage-4.7.2 install. Then I can
{{{
sage: m1 = matrix([1,2]); m1.set_immutable()
sage: m2 = matrix([2,1]); m2.set_immutable()
sage: a = x.ind[m1]; b = 2*x.ind[m2]
sage: a + a
2*x.[1 2]
sage: a + b
x.[1 2] + 2*x.[2 1]
}}}
which is, in my view very cool !
However strange thing has occurred under the hood, in particular for a
strange
reason I don't understand Sage added the two matrices ! This is apparent
in
{{{
sage: a = x.ind[Permutation([3,2,1])]; b = 2*x.ind[1]
sage: a+b
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)
/home/data/Sage-Install/sage-4.7.2/devel/sage-
review/sage/symbolic/<ipython console> in <module>()
/home/florent/src/Sage/sage/local/lib/python2.6/site-
packages/sage/structure/element.so in
sage.structure.element.RingElement.__add__
(sage/structure/element.c:11488)()
/home/florent/src/Sage/sage/local/lib/python2.6/site-
packages/sage/symbolic/expression.so in
sage.symbolic.expression.Expression._add_
(sage/symbolic/expression.cpp:11082)()
2186 relational_operator(_right._gobj))
2187 else:
-> 2188 x = gadd(left._gobj, _right._gobj)
2189 return new_Expression_from_GEx(left._parent, x)
2190
/home/florent/src/Sage/sage/local/lib/python2.6/site-
packages/sage/structure/element.so in
sage.structure.element.RingElement.__sub__
(sage/structure/element.c:11816)()
/home/florent/src/Sage/sage/local/lib/python2.6/site-
packages/sage/structure/coerce.so in
sage.structure.coerce.CoercionModel_cache_maps.bin_op
(sage/structure/coerce.c:7489)()
TypeError: unsupported operand parent(s) for '-': '<class
'sage.combinat.permutation.Permutation_class'>' and 'Integer Ring'
}}}
To make thing crystal clear (I hope):
{{{
sage: class bla(SageObject):
... def __add__(self, other):
... print "Addition called"
sage: a, b = x.ind[m1],2*x.ind[m2]
sage: m1 = bla()
sage: m2 = bla()
sage: m1 + m2
Addition called
sage: m1*m2
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)
/home/data/Sage-Install/sage-4.7.2/devel/sage-
review/sage/symbolic/<ipython console> in <module>()
TypeError: unsupported operand type(s) for *: 'bla' and 'bla'
}}}
WTF ! Why is it adding or multiplying my indices for nothing ! It is a
problem
of Ginac ? of the wrapper ? or behind the chair and the screen ?
Any help greatly appreciated !
Cheers,
Florent
PS: crosspost on sage-devel.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11576#comment:6>
Sage <http://www.sagemath.org>
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