#15025: automatically injected function does not work with desolve
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Reporter: dkrenn | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.4
Component: symbolics | Resolution:
Keywords: desolve function | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by tmonteil):
A similar problem was just hit on [http://ask.sagemath.org/question/25641
/typeerror-in-creating-ode-variable/ this ask question].
The bug is about wrong variable injection (the value injected into the
Python variable does not correspond to the returned value, while it is
claimed), not about `desolve`:
{{{
sage: z = function('y', x)
sage: y
y
sage: z
y(x)
sage: y == z
False
sage: type(y)
<class 'sage.symbolic.function_factory.NewSymbolicFunction'>
sage: type(z)
<type 'sage.symbolic.expression.Expression'>
}}}
Besides fixing this bug, i have nothing against removing automatic
variable injection from Sage (which seems to concern only `var()` and
`function()`), since it creates a lot of confusion between symbolic and
Python variables among new users, for example we can see a lot of
{{{var('n') ; n=2}}} on ask.sagemath.org, as if `var()` was a kind of
variable declaration.
As for the `NewSymbolicFunction` vs `Expression` issue depending on the
arguments of `function()`, our options are:
- create two distinct Python functions for the two situations,
- deprecate the use of `function('y', x)`,
- do not touch anything and provide a better documentation in the
`function()` function.
I like the second one since it goes towards better consistency. But, as
for removing the ugly `var()` (or even the ugly `RR` that breaks the
`RDF`, `RIF`, `RLF` naming scheme and causes meaningless discussions about
whether `Infinity` or `NaN` belong to it), i expect not everyone to agree,
even if this would help newcomers to grasp Sage's logic.
--
Ticket URL: <http://trac.sagemath.org/ticket/15025#comment:5>
Sage <http://www.sagemath.org>
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