convert not coerce padics symbolic function arguments

[rwst]

This affects authors of function code but shows also in:

sage: binomial(Qp(5)(8),3)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-1-43da6d5c56db> in <module>()
----> 1 binomial(Qp(Integer(5))(Integer(8)),Integer(3))

/home/ralf/sage/src/sage/symbolic/function.pyx in sage.symbolic.function.GinacFunction.__call__ (build/cythonized/sage/symbolic/function.cpp:9048)()
    842             (0, Integer Ring)
    843         """
--> 844         res = super(GinacFunction, self).__call__(*args, **kwds)
    845 
    846         # Convert to Integer if the output was of type "int" and any of

/home/ralf/sage/src/sage/symbolic/function.pyx in sage.symbolic.function.BuiltinFunction.__call__ (build/cythonized/sage/symbolic/function.cpp:10572)()
    991             res = self._evalf_try_(*args)
    992             if res is None:
--> 993                 res = super(BuiltinFunction, self).__call__(
    994                         *args, coerce=coerce, hold=hold)
    995 

/home/ralf/sage/src/sage/symbolic/function.pyx in sage.symbolic.function.Function.__call__ (build/cythonized/sage/symbolic/function.cpp:6301)()
    485                             nargs[i] = SR.coerce(carg)
    486                         except Exception:
--> 487                             raise TypeError, "cannot coerce arguments: %s"%(err)
    488                 args = nargs
    489         else: # coerce == False

TypeError: cannot coerce arguments: no canonical coercion from 5-adic Field with capped relative precision 20 to Symbolic Ring

test.

CC: @jdemeyer

Component: symbolics

Author: Ralf Stephan

Branch/Commit: u/rws/builtinfunction_doesn_t_pass_non_sr_coercible_arguments_to_function_code @ e4a30b6

Issue created by migration from https://trac.sagemath.org/ticket/17790

[rwst]

comment:1

So, either it's a problem of p-adics not being coercible into SR (which they should be?), or there should not be coercion but conversion in function.pyx.

[rwst]

Branch: u/rws/builtinfunction_doesn_t_pass_non_sr_coercible_arguments_to_function_code

[rwst]

Commit: f6e2113

[rwst]

Author: Ralf Stephan

[rwst]

comment:3

It was the latter alternative, as there is no coercion. Please review.

---

New commits:

f6e2113

17790: add padics to the conversion workaround for symbolic function arguments

[rwst]

comment:4

The recent #17852 makes binomial(Qp(2)(9),5) fail in this branch with TypeError: function did not return a symbolic expression or an element that can be coerced into a symbolic expression. Reason: rings.arith.binomial now returns (correctly) 1 + 5 + 2*5^2 + O(5^20) instead of 56.

So what should Function do when self.eval returns something not coercible?

[rwst]

comment:5

@jdemeyer, what reason is there in the respective snippet of Function::__call__ l.478-491 not to do the following:

                nargs = [None]*len(args)
                for i in range(len(args)):
                    carg = args[i]
                    try:
                        nargs[i] = SR.coerce(carg)
                    except Exception:
                        nargs[i] = SR(carg)

i.e. not throwing at all. I keep needing exceptions like the Qp of this ticket.

Do we have a fundamental problem here? Why can rings.arith... handle this differently?

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

89f5b2d	Merge branch 'develop' into t/17790/builtinfunction_doesn_t_pass_non_sr_coercible_arguments_to_function_code
9a29cd1	17790: try coercion then conversion

[sagetrac-git]

Changed commit from f6e2113 to 9a29cd1

[sagetrac-git]

Changed commit from 9a29cd1 to e4a30b6

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

e4a30b6

Merge branch 'develop' into t/17790/builtinfunction_doesn_t_pass_non_sr_coercible_arguments_to_function_code

[fchapoton]

comment:10

one failing doctest see patchbot report

[rwst]

comment:12

I think this ticket is wontfix because a better solution would be to write a global Python function accepting everything (as in rings.arith...) and dispatch to the symbolic function for symbolic arguments.

In the ticket case just do

sage: from sage.arith.misc import binomial
sage: binomial(Qp(5)(8),3)
1 + 5 + 2*5^2 + O(5^20)