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The subs method for polynomi

The subs method for polynomipolynomials is not an analog of SR.subs !

sage: a=SR.var("a")
sage: R1.<x>=SR[]
sage: R2.<y,z>=SR[]
sage: x.subs?


prints

Docstring:
Identical to "self(*x)".

See the docstring for "__call__()".

EXAMPLES:

sage: R.<x> = QQ[]
sage: f = x^3 + x - 3
sage: f.subs(x=5)
127
sage: f.subs(5)
127
sage: f.subs({x:2})
7
sage: f.subs({})
x^3 + x - 3
sage: f.subs({'x':2})
Traceback (most recent call last):


etc... Compare with :

sage: y.subs?
Signature:      y.subs(fixed=None, **kw)
Docstring:
Fix some given variables in a given multivariate polynomial and
return the changed multivariate polynomials. The polynomial itself
is not affected. The variable, value pairs for fixing are to be
provided as a dictionary of the form "{variable: value}".

This is a special case of evaluating the polynomial with some of
the variables constants and the others the original variables.

INPUT:

* "fixed" - (optional) dictionary of inputs

* "**kw" - named parameters

OUTPUT: new "MPolynomial"

EXAMPLES:

sage: R.<x,y> = QQbar[]                                                     # optional - sage.rings.number_field
sage: f = x^2 + y + x^2*y^2 + 5                                             # optional - sage.rings.number_field
sage: f((5, y))                                                             # optional - sage.rings.number_field
25*y^2 + y + 30
sage: f.subs({x: 5})                                                        # optional - sage.rings.number_field
25*y^2 + y + 30


As far as I understand it, (a*x).subs(a=1) should have raised an error.

Consider yelping on sage-support...

HTH,