[Libreoffice-bugs] [Bug 44076] =(-8)^(1/3) should return -2

[bugzilla-daemon at bugs.documentfoundation.org]

https://bugs.documentfoundation.org/show_bug.cgi?id=44076

Jean-Baptiste Faure <jbfaure at libreoffice.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jbfaure at libreoffice.org

--- Comment #21 from Jean-Baptiste Faure <jbfaure at libreoffice.org> ---
Why did you implement mathematical inconsistency in Calc? Because MS did the
same in Excel?
Now a^b != exp(b*ln(a))

And computing (-8)^x with x -> 1/3 gives

0,3               #NUM !
0,33              #NUM !
0,333             #NUM !
0,3333            #NUM !
0,33333           #NUM !
0,333333          #NUM !
0,3333333         #NUM !
0,33333333        #NUM !
0,333333333       #NUM !
0,3333333333      #NUM !
0,33333333333     #NUM !
0,333333333333    #NUM !
0,3333333333333   #NUM !
0,33333333333333  #NUM !
0,333333333333333 -2

The last result is wrong because 0,333333333333333 != 1/3
Even better:
0,333333333333334 -2 :-(

And the function f(x) = (-8)^x is not continuous.

You are confusing cubic root and the exponentiation function. a^b is not
defined for a ≤ 0

I am interesting to know a use case where we have to compute the cubic root of
a negative number without knowing in advance that the number is negative.

Best regards. JBF

-- 
You are receiving this mail because:
You are the assignee for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/libreoffice-bugs/attachments/20210811/08a410c1/attachment.htm>