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MathGroup Archive 1993

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Integration bug?

  • To: mathgroup at thnext.mit.edu
  • Subject: Integration bug?
  • From: Robert Singleton <bobs at thnext.mit.edu>
  • Date: Thu, 1 Apr 93 13:32:14 -0500

Hello,

Does anyone know what's going on here? I do the following integral


In[14]:=
  Integrate[Log[x]/((x-y)(x-z)),{x,0,Infinity}]
Out[14]=
  0

So this vanishes for every y and z. This seemed funny to me so I
tried y=1 and z=2. Here is what I got


In[15]:=
  Integrate[Log[x]/((x-1)(x-2)),{x,0,Infinity}]
Out[15]=
       1 2
  -Log[-]
       2
  --------
     2

What's going on?!? I got the following answer for

In[16]:=
  Integrate[Log[x]/((x+y)(x+z)),{x,0,Infinity}]
Out[16]=
         2         2
  -Log[y]  + Log[z]
  ------------------
      2 (-y + z)

I've checked this from tables and I believe it's correct. So Mma is 

doing something right. But what? I suspect the trouble is in Mma
not knowing whether y and z are positive or negative. But I'm not 

sure. Any help would be greatly appreciated. thanks.


bob singleton
bobs at thnext.mit.edu





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