Re: Strange behaviour of Fourier[] in Mathematica 7 (Follow up)
- To: mathgroup at smc.vnet.net
- Subject: [mg94065] Re: Strange behaviour of Fourier[] in Mathematica 7 (Follow up)
- From: "sjoerd.c.devries at gmail.com" <sjoerd.c.devries at gmail.com>
- Date: Thu, 4 Dec 2008 07:13:12 -0500 (EST)
- References: <ggr257$e5r$1@smc.vnet.net> <gh5nr6$of1$1@smc.vnet.net>
Guy, Did they tell you anything about the expected release date for this fix? Cheers -- Sjoerd On Dec 3, 12:42 pm, "Guy Lamouche" <noem... at noemail.com> wrote: > Just received an email from Wolfram saying that the issue is fixed. > Satisfying to see that this was handled rapidly. I assume that the > correction will be integrated in the next release. > > Cordially. > > Guy Lamouche > > "Guy Lamouche" <noem... at noemail.com> wrote in message > > news:ggr257$e5r$1 at smc.vnet.net... > > >I came across the following strange behaviour in Mathematica 7 on my > >system. > > > Here is some data generated in an intermediate calculation: > > > data = {-0.00023798861821554878` + 0.` I, > > 0.0006139487084761968` - > > 0.001435108611558083` I, -0.001710424871758314` + > > 0.0069296921181465935` I, > > 0.0019942263545704086` - 0.021565769535630507` I, > > 0.002517554651534451` + > > 0.04381651818448262` I, -0.01220847735732839` - > > 0.05813547502399065` I, > > 0.018746602690952168` + > > 0.050324001393803136` I, -0.01572173179907872` - > > 0.028359695723765642` I, > > 0.007974058406218107` + > > 0.010364643233016675` I, -0.0025342667815659334` - > > 0.0024424248976939247` I, 0.`, 0.`, 0.`, 0.`, 0.`, 0.`, 0.`, 0.`, > > 0.`, 0.`, 0.`} > > > If I compute the discrete Fourier transform by applying directly the > > formula > > used by Mathematica (as described in the documentation for Fourier), I = get > > a > > nice transform with real and imaginary parts (the following is not > > intended > > to be read, but pasted in Mathematica front-end): > > > n = Length[data]; > > u[s_] = 1/Sqrt[n] \!\( > > \*UnderoverscriptBox[\(\[Sum]\), \(r = > > 1\), \(n\)]\(data[\([\)\(r\)\(]\)]\ Exp[ > > I\ 2. \[Pi] \((r - 1)\) \((s - 1)\)/n]\)\); > > dataTF1 = Table[u[i], {i, 1, n}]; > > ListPlot[{dataTF1 // Re, dataTF1 // Im}, PlotRange -> All, > > PlotStyle -> {Blue, Red}] > > > If I use Fourier[], the imaginary part is put to zero!!! > > > dataTF2 = Fourier[data]; > > ListPlot[{dataTF2 // Re, dataTF2 // Im}, PlotRange -> All, > > PlotStyle -> {Blue, Red}] > > > This behaviour occurs on my system only for some data like the one abov= e, > > but it does occur. There is no problem with 6.0.3 on another computer > > since > > the result is the same for both calculations above. > > > I would like to know if this happens also on other's computer with > > Mathematica 7? I am using the windows version ("7.0 for Microsoft Windo= ws > > (32-bit) (November 10, 2008)") under Vista Business SP1. > > > Thanks in advance. > > > Guy Lamouche