On Friday, March 25, 2011 9:35:13 PM UTC-7, Surendran Karippadath wrote:
>
> If the multiplication sign * is absent ( say by mistake!) what is SAGE
> evaluating?
> For example:
> x=var('x');f=1/((x-1)(x-3));
> f.limit(x=1) returns -1/3
> diff(f,x) returns -1/(x - 4)^2
> plot(f,(x,0,10)) plots a smooth curve going through -1/3.
>
> It is clear it is evaluating f =1/(x-4). How? Why is not pointing to
> the possible error?
>
I think it's taking the expression (x-1), treating it as a symbolic
expression, and plugging in (x-3) for x, thus obtaining (x-3-1) = (x-4).
Actually, here's what happens when I do this:
sage: x=var('x');f=1/((x-1)(x-3));
/Applications/sage/local/lib/python2.6/site-packages/IPython/iplib.py:2073:
DeprecationWarning: Substitution using function-call syntax and unnamed
arguments is deprecated and will be removed from a future release of Sage;
you can use named arguments instead, like EXPR(x=..., y=...)
exec code_obj in self.user_global_ns, self.user_ns
sage: f
1/(x - 4)
If you didn't see the warning, what version of Sage are you using?
--
John
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