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Cute Log Series Bug

  • To: mathgroup at (Mathematica User's Group)
  • Subject: Cute Log Series Bug
  • From: Keith Clay <clay at>
  • Date: Fri, 23 Jul 93 10:08:06 MDT

I have no idea what is happening here, but I thought I should send a copy
of this output.  Evidently there is a bug in Series or Log:

In[1]:= Series[ Log[x(1+x)], {x,0,1} ] 

Out[1]= Log[x] + O[x]                               <- WRONG!

In[2]:= Series[ Log[x(1+x)], {x,0,2} ] 

                     x        3
Out[2]= Log[x] + x - -- + O[x]                      <- Yes.  Notice the
                     2                                       Order(x) part.

In[3]:= Series[ PowerExpand[Log[x(1+x)]], {x,0,1}]

Out[3]= Log[x] + x + O[x]                           <- PowerExpand works, too.

Any explanations?  Strange, in any case.

clay at

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