#10483: Deprecate the misuse of symbolic variables as polynomial variable
--------------------------------+-------------------------------------------
Reporter: SimonKing | Owner: AlexGhitza
Type: defect | Status: new
Priority: major | Milestone: sage-4.6.1
Component: basic arithmetic | Keywords: deprecation symbolic polynomial
variable
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Relatively often on sage-support, users run into a problem since they mix
symbolics and polynomials. Typically, they do
{{{
sage: z = var('z')
sage: P = QQ[z]
}}}
and expect that `z` is the generator of `P` - which is of course
wrong and will soon mean trouble.
I find even worse that one can do
{{{
sage: QQ[x,gap,singular]
Multivariate Polynomial Ring in x, Gap, Singular over Rational Field
}}}
since the variable names are obtained from the string representation of
the given objects.
It should be clear that the preferred way of constructing a polynomial (or
quotient) ring together with its generators is
{{{
sage: R.<x,y,z> = QQ[]
}}}
Hence, it is quite amazing that in the documentation one occasionally
finds the "wrong" usage
{{{
sage: x,y,z = var('x y z')
sage: P = QQ[x,y,z]
}}}
I suggest to deprecate the possibility of providing the variable names by
anything but strings (potentially plus an integer, like
`PolynomialRing(QQ,'x',5)`).
With my patch, one has
{{{
sage: QQ[x,gap,singular]
/mnt/local/king/SAGE/sage-4.6/local/bin/sage-ipython:1:
DeprecationWarning: (Since Sage Version 4.6.1) Variable name 'x' should be
a string, but we obtained <type 'sage.symbolic.expression.Expression'>.
In an interactive session, you should use a definition of the form
'R.<x,y,z>=QQ[]'.
#!/usr/bin/env python
/mnt/local/king/SAGE/sage-4.6/local/bin/sage-ipython:1:
DeprecationWarning: (Since Sage Version 4.6.1) Variable name 'Gap' should
be a string, but we obtained <class 'sage.interfaces.gap.Gap'>.
In an interactive session, you should use a definition of the form
'R.<x,y,z>=QQ[]'.
#!/usr/bin/env python
/mnt/local/king/SAGE/sage-4.6/local/bin/sage-ipython:1:
DeprecationWarning: (Since Sage Version 4.6.1) Variable name 'Singular'
should be a string, but we obtained <class
'sage.interfaces.singular.Singular'>.
In an interactive session, you should use a definition of the form
'R.<x,y,z>=QQ[]'.
#!/usr/bin/env python
Multivariate Polynomial Ring in x, Gap, Singular over Rational Field
}}}
I am not sure what component this ticket belongs. I try basic arithmetic.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10483>
Sage <http://www.sagemath.org>
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