GNU bug report logs - #24561
Unmathematical bc exponentiation behavior

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: "Martens, Tobias" <tobias.martens <at> stud.uni-goettingen.de>
To: "bug-coreutils <at> gnu.org" <bug-coreutils <at> gnu.org>
Subject: Unmathematical bc exponentiation behavior
Date: Wed, 28 Sep 2016 15:48:27 +0000

[Message part 1 (text/plain, inline)]

Hey,

echo "-(1)^2" | bc
1

I would have expected -1. This behavior is unmathematical and very confusing, because otherwise bc acts quite logic.
Not sure if it is mandated by POSIX, atleast I could not find it to be in the section of exponentiation operator. Was this ever discussed?
Resolving "-(positive float)" to "(-1)*(positive float)" for intern calculation seems more appropriate to me and would give the desired results.

[Message part 2 (text/html, inline)]

Message #8 received at 24561 <at> debbugs.gnu.org (full text, mbox):

From: Andreas Schwab <schwab <at> linux-m68k.org>
To: "Martens\, Tobias" <tobias.martens <at> stud.uni-goettingen.de>
Cc: 24561 <at> debbugs.gnu.org
Subject: Re: bug#24561: Unmathematical bc exponentiation behavior
Date: Wed, 28 Sep 2016 20:10:15 +0200

On Sep 28 2016, "Martens, Tobias" <tobias.martens <at> stud.uni-goettingen.de> wrote:

> echo "-(1)^2" | bc
> 1
>
> I would have expected -1. This behavior is unmathematical and very confusing, because otherwise bc acts quite logic.
> Not sure if it is mandated by POSIX

Unary - has higher precedence than ^, thus it is parsed as (-(1))^2.

Andreas.

-- 
Andreas Schwab, schwab <at> linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Message #11 received at 24561 <at> debbugs.gnu.org (full text, mbox):

From: Bernhard Voelker <mail <at> bernhard-voelker.de>
To: "Martens, Tobias" <tobias.martens <at> stud.uni-goettingen.de>,
 24561 <at> debbugs.gnu.org
Subject: Re: bug#24561: Unmathematical bc exponentiation behavior
Date: Wed, 28 Sep 2016 23:18:10 +0200

tag 24561 notabug
close 24561
stop


On 09/28/2016 05:48 PM, Martens, Tobias wrote:
> echo "-(1)^2" | bc
> 1

Andreas already gave the answer: operator precedence (see 'man bc').
Besides, bc(1) is not part of GNU coreutils, and a better address for
such a report would have been "bug-bc <at> gnu.org".
Therefore, I'm marking this as 'not a bug' here, closing the issue.

Have a nice day,
Berny

Message #14 received at 24561 <at> debbugs.gnu.org (full text, mbox):

From: Erik Auerswald <auerswal <at> unix-ag.uni-kl.de>
To: "Martens, Tobias" <tobias.martens <at> stud.uni-goettingen.de>
Cc: 24561 <at> debbugs.gnu.org
Subject: Re: bug#24561: Unmathematical bc exponentiation behavior
Date: Thu, 29 Sep 2016 08:52:46 +0200

Hi Tobias,

On Wed, Sep 28, 2016 at 03:48:27PM +0000, Martens, Tobias wrote:
> echo "-(1)^2" | bc
> 1
> 
> I would have expected -1. This behavior is unmathematical and very
> confusing, because otherwise bc acts quite logic.

bc did exactly what you asked it to do. You probably meant to write:

    echo "-(1^2)" | bc

Thanks,
Erik
-- 
If it ain't broke, don't fix it.

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