Re: Nasty bug in Integrate (version 5.0)
- To: mathgroup at smc.vnet.net
- Subject: [mg45926] Re: Nasty bug in Integrate (version 5.0)
- From: "David W. Cantrell" <DWCantrell at sigmaxi.org>
- Date: Thu, 29 Jan 2004 05:36:56 -0500 (EST)
- References: <bv83h6$icj$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
mathuser7 at hotmail.com (Math User) wrote:
> Could anyone explain why Mathematica 5.0 is ignoring the term 1/x in
> the first and second answers?
Looks like a bug to me. I'd be interested to know how it came to be.
> In[1]:= Integrate[1/x + x^c, {x, a, b}]
>
> Out[1]= (-a^(1 + c) + b^(1 + c))/(1 + c)
This reminds me that I'm not even happy with
In[1]:= Integrate[x^c, x]]
Out[1]= x^(1 + c)/(1 + c)
because it's incorrect when c is -1. I would have hoped that perhaps
Mathematica would have given something like
If[c == -1, Log[x], x^(1 + c)/(1 + c)]
instead. I also think it strange that one cannot even coax Mathematica
into considering the possibility that c might be -1 by the following
In[2]:= Assuming[c == -1, Integrate[x^c, x]]
Out[2]= x^(1 + c)/(1 + c)
BTW, for Integrate[x^c, x]], I would also say that a better answer than
Mathematica's is
(x^(1 + c) -1)/(1 + c)
because at least we then have it "correct" in the sense that
In[3]:= Limit[(x^(1 + c) - 1)/(1 + c), c -> -1]
Out[3]= Log[x]
David Cantrell