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MathGroup Archive 1997

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Re: [Q] Why Integrate[1/x,x] <> Log[Abs[x]] with Mma 2.2 ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg8761] Re: [mg8699] [Q] Why Integrate[1/x,x] <> Log[Abs[x]] with Mma 2.2 ?
  • From: Olivier Gerard <jacquesg at pratique.fr>
  • Date: Sun, 21 Sep 1997 20:51:05 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

At 08:47 +0200 97.09.19, Denis Barbier wrote:
> Hi all,
>
> it is well known that Integrate[1/x,x] =3D Log[Abs[x]], but Mma 2.2 return=
s
> Log[x].
>
> How can i correct this ?
>
> Thanks in advance
>
>    Denis

Bonjour Denis,

I am afraid that what you call "well-known" could be more
accurately described by "practical and common convention suited
to most real intervals".

There are various common methods to force
Mathematica to give you Log[Abs[x]] in response to Integrate[1/x,x],
for instance:

Unprotect[Integrate];
Integrate[1/x_Symbol,x_Symbol,___Rule]:=3DLog[Abs[x]];
Protect[Integrate];

but I cannot recommend making that because the treatment
of the arguments patterns of Integrate is
organized in an optimized and quite intricate way.
In such a powerful (and knowledge-laden) black box function
as Integrate, tinkering with it can make you loose a lot by
overriding predefined transformations.

I hope nevertheless that this answer will help you in what you
are currently doing.

By the way do you know we have a French Mathematica User Group ?
To join, just send a blank-subject message to

Listserv at ext.jussieu.fr

with the line:

sub GROUMF Your name - Your institution

Moderators are  Eric Lewin and J-C Culioli.

I invite all french speaking users of Mathematica to join in.
We will be pleased to welcome you ! (We welcome the others as
well, but the discussions take place in french)


Olivier Gerard

Editor in Chief - special issues
`Quadrature=B4      <quadrature at technolink.org>
=46rench Mathematics Quarterly





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