Integrating using If[ ]
- To: mathgroup at smc.vnet.net
- Subject: [mg33301] Integrating using If[ ]
- From: michael_chang86 at hotmail.com (Michael Chang)
- Date: Thu, 14 Mar 2002 02:22:04 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
Hi everyone,
While recently trying out my spiffy new version of Mathematica 4.1 for
Windoze XP, I've stumbled upon the following perplexing result.
Suppose I define
In[1]:= x[t_]:=If[t>=0,Exp[-t],Exp[t]];
If I now try and evaluate (a two-sided Laplace Transform)
In[2]:= Integrate[x[t] Exp[-s t],{t,-Infinity,Infinity}]
all I get back is essentially an unevaluated answer. Replacing
{-Infinity, Infinity} by, for instance, {-100,100}, *does* give me an
answer, though.
Typing in
In[3]:= Integrate[Exp[-Abs[t]] Exp[-s t],{t,-Infinity,Infinity}]
however, does give me back a meaningful result with the conditionals
properly stated that -1<Re[s]<1. Why does In[3] work, but not In[1]
and In[2]? Am I foolishly doing something stup!d here?
Michael
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