bug#24561: Unmathematical bc exponentiation behavior

[Erik Auerswald]

Hi Tobias,

On Wed, Sep 28, 2016 at 03:48:27PM +, 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.

bug#24561: Unmathematical bc exponentiation behavior

[Bernhard Voelker]

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...@gnu.org".
Therefore, I'm marking this as 'not a bug' here, closing the issue.

Have a nice day,
Berny

bug#24561: Unmathematical bc exponentiation behavior

[Andreas Schwab]

On Sep 28 2016, "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.
> Not sure if it is mandated by POSIX

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

Andreas.

-- 
Andreas Schwab, sch...@linux-m68k.org
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bug#24561: Unmathematical bc exponentiation behavior

[Martens, Tobias]

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.