On Friday, November 8, 2013 2:21:26 PM UTC-5, PavelY wrote:
>
> I am trying to compute a limit with sage, and I get incorrect answers.
>
> Here is an example which should produce the result of 0 but does not.
>
> reset()
> n = var('n')
>
> assume(n>0)
> series = -(3*n^2 + 1)*(-1)^n/sqrt(n^5 + 8*n^3 + 8)
> working_series = -(7*n^2 + 8)*(-1)^n/sqrt(n^5 + 4*n^2 + 2)
>
> print "Limit of series = "+str(limit(series, n=infinity))
> print "Limit of working_series = "+str(limit(working_series, n=infinity))
>
> This yields these results:
>
> Limit of series = 38/25*pi^2*und
>
Note the "und" - undefined. Maxima is probably noticing the (-1)^n piece...
> Limit of working_series = 0
>
> Both Limits should be equal to zero. Removing the assumption of n>0 or
> adding assume(n,'integer') does not change the outcome.
>
> If someone is aware of why this is happening and/or knows a method to
> solving this; please let me know.
>
> Thank You,
>
> Pavel Y.
>
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