On Dec 3, 12:31 pm, Robert Bradshaw <[EMAIL PROTECTED]>
wrote:
> On Dec 3, 2008, at 12:15 PM, Jason Grout wrote:
>
> > However, mathematical convention says that x is a dummy variable,
> > and so
> > there should be no difference between f(x) = sin(x) and f(y)=sin(y).
> > However, currently, each tramples on different parts of the global
> > namespace.
>
> Mathematically, it's a dummy variable, but implementation-wise there
> is a distinction. Consider
>
> sage: f(x) = sin(x)
> sage: f + x
> x |--> sin(x) + x
>
> sage: f(y) = sin(y)
> sage: f + x
> y |--> sin(y) + x
Yuck; I don't like this. (But there's a lot I don't like about how
the symbolics system conflates functions and expressions, converting
back and forth in a way that feels arbitrary and confusing to me.)
> > I think the preparser ought to return
>
> > sage: preparse('f(x)=sin(x)')
> > '_=sage.calculus.calculus.var("x");f=symbolic_expression(sin
> > (_)).function(_)'
> > sage: f
> > x |--> sin(x)
>
> > (where "_" should be a temporary variable). This way the global
> > namespace is not affected by what conventionally is a dummy variable.
I agree.
> > Simon pointed out that there is precedence for injecting variables
> > that
> > appear on the left side of an equals sign, using "R.<x> = QQ[]" as an
> > example.
>
> > Any comments or thoughts?
>
> I think this is very useful.
I have no idea which "this" you're talking about. (The current
behavior for "R.<x> = ..."? The current behavior for "f(x) = ..."?
Jason's proposed modification for "f(x) = ..."?)
> - Robert
Carl
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