By the way, this is now
http://trac.sagemath.org/sage_trac/ticket/1460
On Dec 11, 2007 8:53 AM, William Stein <[EMAIL PROTECTED]> wrote:
> On Dec 11, 2007 8:39 AM, Joel B. Mohler <[EMAIL PROTECTED]> wrote:
> >
> > Hi,
> >
> > I've noticed a very recent regression -- it worked 2 months ago.
> >
> > sage: t=var('t')
> > sage: f=t*cos(0)
> > sage: float(f(1))
> > 1.0
> > sage: f=t*sin(0)
> > sage: float(f(1))
> > Traceback...
> > <type 'exceptions.TypeError'>: float() argument must be a string or a number
> >
> > --
>
> It is actually hard to decide how to fix this. This is a result of
> several significant fixes
> and optimizations recently. What is happening is that for t*sin(0)
> the simplified
> form is 0, so (t*sin(0)).variables() is [].
>
> sage: t=var('t')
> sage: f = t*cos(0)
> sage: f.variables()
> (t,)
> sage: g = t*sin(0)
> sage: g.variables()
> ()
> sage: float(f(1))
> 1.0
> sage: float(g(t=1))
> 0.0
>
> Both f(1) and g(1) are formal products. However:
>
> sage: g(1)._operands
> [t, 0]
> sage: f(1)._operands
> [1, 1]
>
> Notice the [t, 0].
>
> One possible solution would be to call simplify before
> doing float(...) -- but that could greatly slow symbolic calculus
> down in some cases. Another possibility would be to change
> the definition of variables() to return all variables, even the ones
> that are simplified away:
>
> sage: (x - x).variables() # fake
> (x,)
>
> That would be very confusing.
>
> A third possibility would be to make implicit calling use variables
> in the unsimplified expression if the simplified expression has
> no variables. This would cleanly deal with your case above.
>
> Thoughts?
>
> -- William
>
--
William Stein
Associate Professor of Mathematics
University of Washington
http://wstein.org
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