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Re: Taking the Log causing Mathematica kernel crash.
*To*: mathgroup at smc.vnet.net
*Subject*: [mg57089] Re: Taking the Log causing Mathematica kernel crash.
*From*: Bill Rowe <readnewsciv at earthlink.net>
*Date*: Sun, 15 May 2005 03:03:43 -0400 (EDT)
*Sender*: owner-wri-mathgroup at wolfram.com
On 5/14/05 at 4:57 AM, nma at 12000.org (Nasser Abbasi) wrote:
>"me" <nma at 12000.org> wrote in message
>news:d615dg$nn1$1 at smc.vnet.net...
>>Mathematica 5.1 on Windows.
>This is another small variation on this problem of the Log[]
>Now, this causes Mathematica kernel to start eating all the memory
>very quickly with full CPU consumption.
>Clear["Global`*"]
>f[t_] := Sin[3.5*t] + 2*Cos[2*t];
>g[t_] := Piecewise[{{0, t < -2*Pi}, {f[t], t >= -2*Pi && t <= 2*Pi},
>{0, t > 2*Pi}}];
>c[w_] := Integrate[g[t]*Exp[(-I)*w*t], {t, -Infinity, Infinity}];
>Plot[20*Log[10, Abs[c[w]]^2 +0.01], {w, -5, 5}, PlotRange -> All]
I don't think hte problem is with the Log function nor with any of the other functions you are using here.
Try using NIntegrate instead of Integrate.
Consider. The plot of c[w] has several lobes. Consequently, Plot needs to evaluate c[w] a fairly large number of times in order to achieve a valid representation of c[w]. By using Integrate, you are asking Mathematica to perform a symbolic integration every time c[w] is evaluated. This requires more memory for every evaluation of c[w] than a numeric evaluation. And this is most likely the cause of the crash.
In addition to using less memory, redefining c[w] with NIntegrate instead of Integrate things will run faster.
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