Re: [libreoffice-users] Awkward behaviour of LO Calc

Hi,

lorieul schrieb:
> Hello to all,
>
> I have found a fancy behavior of Calc but I cannot decide whether it is
> a bug or a "feature". Hence I was looking for your advice before posting
> a bug report (if required).

That is good. It is 
https://bugs.documentfoundation.org/show_bug.cgi?id=37271

>    1. Open LO Calc
>    2. In A1 enter formula "=1-2^2" and press enter key
>       The result shown is -3 which is ok since
>       1-2² = 1-(2²) = 1-4 = -3
>    3. In A2 enter formula "=-2^2" and press enter key
>       I would expect this to be treated as -2² = -(2²) = -4
>       But Calc considers it as (-2)² = +4
>       Quite obviously, a work around is to define the formula as
>       "=-(2^2)" which indeed returns -4
>
> I've checked the wiki page dedicated to operators [1] but it does not
> give much information on operator precedence.
>
>  From my standpoint, both examples show an inconsistent behavior of Calc.
> For me, either we should have both 1-2^2 = 1+4 = 5 and -2^2 = +4
> Or we should have both 1-2^2 = 1-4 = -3 and -2^2 = -4

A minus can be a binary operator subtraction or a unary operator sign.
In "=1-2^2" there is a operand left and right of the minus, so it is a 
binary operator. This means calculate its operands and then subtract.
In "=-2^2" there is no operand left. Therefore the minus can only be a 
unary operator, which means, it is a sign of the number. So Calc takes 
the number -2 and puts it to the power 2.

> However, perhaps some of you have a different view point on the matter ?
> In other words, is that a bug or is it perfectly normal ?

It is no bug, but a bad UI, because pupils are thought, that -2² is -4. 
One solution to fit common understanding to the formal term 
interpretation you can see in Gnumeric. It simple does not allow it. 
When the user enters =-2^2 it automatically adds brackets, so that it 
becomes (-2)^2 and the users knows the meaning unambiguous.

To force a result of -4 you need to tell Calc, that the minus is a 
binary operator. The formula "=0-2^2" would do that.

> Of course changing such behavior will cause a hell lot of trouble in
> existing documents… but perhaps the operator precedence should be
> explicitly specified on the wiki ?

The precedence is defined in ODF 
http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part2.html#Operators

Kind regards
Regina


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