#20312: parent of argument lost with Functions
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Reporter: rws | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-7.2
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Description changed by rws:
Old description:
> Except for some classes, Python objects as function arguments are coerced
> into SR, but with `GinacFunction`s the parent gets lost, i.e. the result
> is not converted back. Ths violates the rule that function input and
> output should be of the same type.
> {{{
> sage: S.<y> = PolynomialRing(RR)
> sage: ex = sin(asin(y)); ex
> y
> sage: type(ex)
> <type 'sage.symbolic.expression.Expression'>
> sage: ex.is_symbol()
> True
> }}}
> This also shows that the notion "SR encapsulates all Sage objects" is
> wrong because everything coerces into SR. SR only encapsulates certain
> "numeric" objects. Pynac can't be blamed as it only sees expressions. The
> problem is in `symbolic/function.pyx` where the parent of function
> arguments is lost.
>
> See also #18832
New description:
Except for some classes, Python objects as function arguments are coerced
into SR, but with `GinacFunction`s as well as with `BuiltinFunction`s the
parent gets lost, i.e. the result is not converted back. Ths violates the
rule that function input and output should be of the same type.
{{{
sage: S.<y> = PolynomialRing(RR)
sage: ex = sin(asin(y)); ex
y
sage: type(ex)
<type 'sage.symbolic.expression.Expression'>
sage: ex.is_symbol()
True
}}}
This also shows that the notion "SR encapsulates all Sage objects" is
wrong because everything coerces into SR. SR only encapsulates certain
"numeric" objects. Pynac can't be blamed as it only sees the coerced
expressions. The problem is in
`symbolic/function.pyx:BuiltinFunction.__call__` where the parent of
function arguments is lost.
See also #18832 and maybe #17790.
--
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Ticket URL: <http://trac.sagemath.org/ticket/20312#comment:3>
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