MathGroup Archive 1992

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Re: Upgrades that aren't (old and new bugs).


Paul McGuire writes:

> On newer versions of Mathematica the cube root of -1 is no longer -1 but
> has become the complex cube root of -1 with the least positive argument.
> 
> N[(-1)^(1/3)]
> 0.5 + 0.866025 I 
> 
> This messes up  the internal structure and built in routines of Mathematica

In Version 1.2, odd roots along the negative real axis were handled as
a special case, unlike any other roots.  This sort of inconsistent
treatment of branch cuts, as with the V1.2 transformation Sqrt[x^2] ==> x,
causes a number of serious problems in the internal routines and elsewhere,
and has been corrected for V2.0.

Rules attached to Power can generally be used to get V1.2 behavior
for these roots.

Dave Withoff
withoff at wri.com





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