On Thu, Mar 12, 2009 at 4:34 PM, William Stein <wst...@gmail.com> wrote:
>
> On Thu, Mar 12, 2009 at 2:19 PM, Ondrej Certik <ond...@certik.cz> wrote:
>>
>> On Thu, Mar 12, 2009 at 1:36 PM, Jose Guzman <n...@neurohost.org> wrote:
>>>
>>> Dear colleagues,
>>>
>>> I've just discovered this wonderful thing called Sage (I am a completely
>>> newbie, my apologizes in advance...), and I have to admit that I am
>>> impressed with Sage!!!. I started yesterday, and came along the tutorial
>>> already. I still miss some more documentation...specially related with
>>> worksheet use/configuration (I did not find any other way to combine
>>> LaTeX, html and sage to create nice worksheets like the ones I saw
>>> today. I simply start a cell with %htmlo %latex or %sage).
>>>
>>> Anyway, I was playing around with the limits, and after checking the
>>> short tutorial
>>> (http://sage.math.washington.edu/home/elliottd/calctut/limits.html) I
>>> wanted to try something by myself. I found the following inconvenience.
>>>
>>>
>>> sage: g=9.81
>>> sage: t=var('t')
>>> sage: limit(2*g*(t^2-1)/(t-1),t=1)
>>> >>> gives me 39
>>>
>>> However, if I simplify the equation and calculate the limit...
>>> sage: limit(2*g*(t+1),t=1)
>>> >> gives me the good value 39.276
>>
>> I think the good value should actually be:
>>
>> In [4]: limit(2*g*(t**2-1)/(t-1), t, 1)
>> Out[4]: 39.24
>
> And here is how one can get the above entirely in Sage using a modern
> symbolic manipulation library called sympy that's included in Sage :-)
>
> teragon:sage-3.4.alpha0 wstein$ sage
> ----------------------------------------------------------------------
> | Sage Version 3.4, Release Date: 2009-03-11 |
> | Type notebook() for the GUI, and license() for information. |
> ----------------------------------------------------------------------
> sage: g=9.81
> sage: import sympy
> sage: t = sympy.var('t')
> sage: sympy.limit(2*g*(t^2-1)/(t-1),t,1)
> 39.2400000000000
In fact, you can just do:
sage: g=9.81
sage: var('t')
sage: import sympy
sage: sympy.limit(2*g*(t^2-1)/(t-1), t, 1)
Ondrej
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