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MathGroup Archive 2005

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Re: Taking the Log causing Mathematica kernel crash.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg57055] Re: [mg57051] Taking the Log causing Mathematica kernel crash.
  • From: zhengji.li at t3gt.com
  • Date: Fri, 13 May 2005 01:18:49 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

You may have made some mistakes. Maybe you mean this(it works well):
Clear["Global`*"]
f[t_] := Sin[3.5 t] + 2 Cos[2 t];
g[t_] := Piecewise[{{0, t < -2Pi}, {f[t], t >= -2Pi && t <= 2Pi},
                    {0, t > 2Pi}}];
c[w_] = Integrate[g[t] Exp[-I w t], {t, -Infinity, Infinity}]; (* Fourier
Transform*)
Plot[20 Log[10, Abs[c[w]]], {w, -5, 5}, PlotRange -> All]

1. The definition of g[t] is wrong.
2. c[w_] = ... but not c[w_] := ...
                                                                                                                                       
                      "me"                                                                                                             
                      <nma at 12000.org>          To:       mathgroup at smc.vnet.net                                                        
                                               cc:                                                                                     
                      05, 13, 2005             Subject: [mg57055]  [mg57051] Taking the Log causing Mathematica kernel crash.                    
                      10:44 AM                                                                                                         
                      Please respond to                                                                                                
                      "me"                                                                                                             
                                                                                                                                       
                                                                                                                                       




Mathematica 5.1 on Windows.

Clear["Global`*"]
f[t_] := Sin[3.5 t] + 2 Cos[2 t];
g[t_] := Piecewise[{{0, t < -2Pi}, { f[t], t = -2Pi && t = 2Pi}, {0, t >
2Pi}}];
c[w_] := Integrate[ g[t] Exp[-I w t], {t, -Infinity, Infinity}] ;
Plot[20 Log[10, Abs[c[w]]], {w, -5, 5}, PlotRange -> All]

The above code causes Mathemtica kernel crash.

Change the last line above to remove the Log, then it is OK:

Plot[20 Abs[c[w]], {w, -5, 5}, PlotRange -> All]

Nasser






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