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MathGroup Archive 1999

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RE: Strange results from Integrate

  • To: mathgroup at smc.vnet.net
  • Subject: [mg16065] RE: [mg16022] Strange results from Integrate
  • From: "Ersek, Ted R" <ErsekTR at navair.navy.mil>
  • Date: Tue, 23 Feb 1999 03:45:20 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

Sergio Terrazas:
Reported a problem with Integrate.
______________________

I think he found a problem, but don't agree with some of the results he
posted.  I am using Version 3.0.1 with a Windows 95.  I get the results
below.
 
Out[1], Out[2], Out[3], Out[4], and Out[5] below show the right answers.
______________________

In[1]:=
F[x_]=Integrate[Exp[-20(x-125/10)],x]
Out[1]=
-E^(250 - 20*x)/20

In[2]:=
F[Infinity]-F[126/10]
Out[2]=
1/(20*E^2)

In[3]:=
Integrate[Exp[-20(x-125/10)],{x,126/10,Infinity}]
Out[3]=
1/(20*E^2)

In[4]:=
N[%]
Out[4]=
0.006766764161830635

In[5]:=
NIntegrate[Exp[-20(x-12.5)],{x,12.6,Infinity}]
Out[5]=
0.006766764161830801
__________________

Out[6], Out[7], and Out[8] below show wrong answers.  I can't explain how it
comes up with these answers.


In[6]:=
Integrate[Exp[-20(x-12.5)],{x,126/10,Infinity}]
Out[6]=
0.

In[7]:=
Integrate[Exp[-20(x-125/10)],{x,12.6,Infinity}]
Out[7]=
3.259257562135177*^91

In[8]:=
Integrate[Exp[-20(x-12.5)],{x,12.6,Infinity}]
Out[8]=
3.259257562135177*^91

___________________
Regards,
Ted Ersek


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