Re: Odd behavior (bug?) with Exp[-x^2} and Erf
- To: mathgroup at smc.vnet.net
- Subject: [mg43028] Re: Odd behavior (bug?) with Exp[-x^2} and Erf
- From: Bill Rowe <listuser at earthlink.net>
- Date: Fri, 8 Aug 2003 00:26:43 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
On 8/7/03 at 12:53 AM, peter1963 at totalise.co.uk (Peter Pein) wrote:
> Bill Rowe wrote:
>
> >On 8/4/03 at 12:45 AM, siegman at stanford.edu (AES/newspost) wrote:
> >>Very reluctant to claim I've found a bug in Mathematica, but the
> >>following cells certainly aren't doing what I expect them to:
> >> f[x_] = (Exp[-5(x + 1)^2] + Exp[-5x^2] + Exp[-5(x - 1)^2])^2
> >> Plot[f[x], {x, 0, 2}, PlotRange -> {{0, 2}, {0, 2}}];
> >> g[y_] = Integrate[f[x], {x, 0, y}, Assumptions -> y > 0]
> >> Plot[g[y], {y, 0.001, 2}, PlotRange -> {{0, 2}, {0, 1}}];
> >What do you see that you don't expect?
> since f[x]>0 for real x, nobody would expect g[y] to decrease anywhere.
> P.S.: You might have got the latest version of Mathematica, but 4.x
> shows odd (strange? weird!) behaviour.
When I first looked at this issue, I used version 5.0 and got a result consistent with what I expected. Hence, the question about expectations. It was not until later I realized version 4.x did not produce the same result.