Mathematica Asked by An old man in the sea. on December 1, 2020
Bug introduced in 9.0.0 and fixed in 9.0.1
I’m trying to compute this limit:
Limit[E^-(r^2)^(2*n)*r*2*Pi, n -> Infinity]
But, when I run the code above, Mathematica shuts down. I get a warning from Windows stating that the Mathematica 9 Kernel has stopped working. Mathematica itself gives no warning or message. Why is that?
With
$Version
(* 10.3.0 for Microsoft Windows (64-bit) (October 9, 2015) *)
Mathemeatica returns a limit that depends on r
, as it should.
Plot[Limit[E^-(r^2)^(2*n)*r*2*Pi, n -> Infinity], {r, -2, 2}, AxesLabel -> {r, Lim}]
Addendum
Although Limit
returns unevaluated for arbitrary r
, it can be made to produce useful results by making assumptions on r
. For instance,
Piecewise[{Assuming[{#}, Limit[E^-(r^2)^(2*n)*r*2*Pi, n -> Infinity]], #} & /@
{r < -1, r == -1, -1 < r < 1, r == 1, r > 1}]
(* Piecewise[{{0, r < -1}, {(-2*Pi)/E, r == -1}, {2*Pi*r, -1 < r < 1},
{(2*Pi)/E, r == 1}}, 0] *)
which reproduces the plot above, apart from the discontinuities at r = -1
and r = 1
.
Correct answer by bbgodfrey on December 1, 2020
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