Opened 9 years ago
Last modified 3 years ago
#9935 new defect
Make a symbolic mod function
Reported by: | jason | Owned by: | burcin |
---|---|---|---|
Priority: | major | Milestone: | sage-7.4 |
Component: | symbolics | Keywords: | |
Cc: | burcin, jdemeyer, rws | Merged in: | |
Authors: | Reviewers: | ||
Report Upstream: | N/A | Work issues: | |
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description (last modified by )
A participant in the PREP program noticed that mod is not a symbolic function:
sage: mod(x,4) ERROR: An unexpected error occurred while tokenizing input The following traceback may be corrupted or invalid The error message is: ('EOF in multi-line statement', (4562, 0)) ERROR: An unexpected error occurred while tokenizing input The following traceback may be corrupted or invalid The error message is: ('EOF in multi-line statement', (4530, 0)) ERROR: An unexpected error occurred while tokenizing input The following traceback may be corrupted or invalid The error message is: ('EOF in multi-line statement', (842, 0)) --------------------------------------------------------------------------- TypeError Traceback (most recent call last) /home/grout/sage-4.5.2/devel/sage-main/sage/functions/<ipython console> in <module>() /home/grout/sage/local/lib/python2.6/site-packages/sage/rings/finite_rings/integer_mod.so in sage.rings.finite_rings.integer_mod.Mod (sage/rings/finite_rings/integer_mod.c:2633)() /home/grout/sage/local/lib/python2.6/site-packages/sage/rings/finite_rings/integer_mod.so in sage.rings.finite_rings.integer_mod.IntegerMod (sage/rings/finite_rings/integer_mod.c:2952)() /home/grout/sage/local/lib/python2.6/site-packages/sage/rings/finite_rings/integer_mod.so in sage.rings.finite_rings.integer_mod.IntegerMod_int.__init__ (sage/rings/finite_rings/integer_mod.c:14249)() /home/grout/sage/local/lib/python2.6/site-packages/sage/structure/parent.so in sage.structure.parent.Parent.__call__ (sage/structure/parent.c:6407)() /home/grout/sage/local/lib/python2.6/site-packages/sage/structure/coerce_maps.so in sage.structure.coerce_maps.NamedConvertMap._call_ (sage/structure/coerce_maps.c:4053)() /home/grout/sage/local/lib/python2.6/site-packages/sage/symbolic/expression.so in sage.symbolic.expression.Expression._integer_ (sage/symbolic/expression.cpp:4026)() TypeError: unable to convert x (=x) to an integer
Hopefully it should be easy to wrap mod in a symbolic function, something like:
sage: def eval_mod(self, x): ....: if isinstance(x, (int, Integer)): ....: return mod(x,5) ....: return None ....: sage: f=function('f', eval_func=eval_mod) sage: f(x) f(x) sage: f(13) 3 sage: f(x^2+x+1) f(x^2 + x + 1) sage: f(x^2+x+1).subs(x=2) 2 sage: f(x^2+x+1).subs(x=3) 3 sage: f(x^2+x^3).subs(x=1) 2 sage: f(x^2+x^3).subs(x=2) 2 sage: f(x^2+x^3).subs(x=3) 1
See also http://ask.sagemath.org/question/25037/declaring-variable-to-be-in-a-particular-fieldringgroup/
More discussions: https://groups.google.com/forum/#!searchin/sage-devel/mod|sort:relevance/sage-devel/goNosLk_t9M/xYDgEdIsLYsJ https://groups.google.com/forum/#!searchin/sage-devel/mod|sort:relevance/sage-devel/g7AdhAyQH-k/O1IGYbNRAQAJ
Change History (13)
comment:1 Changed 9 years ago by
comment:2 Changed 9 years ago by
There are plenty of examples in the directory sage/functions/
, just look for classes deriving from BuiltinFunction
. You'll probably want to deprecate the parent
keyword argument to mod()
, so sage.functions.transcendental.Function_exp_integral
might provide a good template.
comment:3 Changed 6 years ago by
- Milestone changed from sage-5.11 to sage-5.12
comment:4 Changed 5 years ago by
- Milestone changed from sage-6.1 to sage-6.2
comment:5 Changed 5 years ago by
- Milestone changed from sage-6.2 to sage-6.3
comment:6 Changed 5 years ago by
- Milestone changed from sage-6.3 to sage-6.4
comment:7 Changed 4 years ago by
- Description modified (diff)
comment:8 Changed 4 years ago by
- Description modified (diff)
comment:9 follow-up: ↓ 12 Changed 3 years ago by
- Cc jdemeyer rws added
We still don't have a good "mod". I would suspect that this has been discussed at length in the past years.
I'm bringing this up because I'm in need of periodic piecewise functions (#21215). Using a suitable symbolic mod would be one way. On Mathematica, using their 3-argument Mod function seems to be the standard way for defining periodic piecewise functions - see for example here: http://community.wolfram.com/groups/-/m/t/156025 We could to the same (one possible route).
comment:10 Changed 3 years ago by
- Milestone changed from sage-6.4 to sage-7.4
comment:11 Changed 3 years ago by
- Description modified (diff)
comment:12 in reply to: ↑ 9 ; follow-up: ↓ 13 Changed 3 years ago by
Replying to mkoeppe:
I'm bringing this up because I'm in need of periodic piecewise functions (#21215). Using a suitable symbolic mod would be one way.
It is the more complicated way. You are asking for a feature of piecewise
which can be had just by the addition of a period
keyword. A symbolic mod
is not necessary for it, and I'm arguing it's not necessary at all because there are no use cases that are handled better in the symbolic ring than in a dedicated finite ring, even if Sage does not have it at the moment. As the user of the ask.sagemath question above finally realized as well.
comment:13 in reply to: ↑ 12 Changed 3 years ago by
Replying to rws:
Replying to mkoeppe:
I'm bringing this up because I'm in need of periodic piecewise functions (#21215). Using a suitable symbolic mod would be one way.
It is the more complicated way. You are asking for a feature of
piecewise
which can be had just by the addition of aperiod
keyword. A symbolicmod
is not necessary for it, and I'm arguing it's not necessary at all because there are no use cases that are handled better in the symbolic ring than in a dedicated finite ring, even if Sage does not have it at the moment. As the user of the ask.sagemath question above finally realized as well.
Thanks!
Burcin, is there a nice example somewhere that we can just copy and modify to make a symbolic function? This sounds like it would be easy for a beginner to do if there was a good example almost like it somewhere.