Around
is a useful feature of Mathematica 12 to work with uncertain data.
x = Around[-1, {0.5, 1.5}]
$-1.0^{+1.5}_{-0.5}$
I'm curious how to get an absolute value of such uncertain data.
When I use Abs
directly I get an unexpected result:
Abs[x]
$1.0^{+1.5}_{-0.5}$
I have expected: $1.0^{+0.5}_{-1.0}$, because
Abs[x["Interval"]]
Interval[{0, 1.5}]
In total there are two issues:
Upper and lower uncertainties are not interchanged when taking
Abs
.Crossing of zero is ignored.
Is this intended behaviour of Around
or some sort of a bug?
How should I calculate absolute values of uncertain data points? For example, when I want to plot Abs
of uncertain of data?
Update
Simple multiplication by a negative number gives incorrect result:
(-1)*x
$1.0^{+1.5}_{-0.5}$ (* Correct answer is $1.0^{+0.5}_{-1.5}$*)
Around
is pretty new and apparently very buggy. Or the two uf us haven't understood the deeper meaning ofAround
, yet. $\endgroup$Abs
doesn't supportAround
in its initial implementation (unless it is documented to do so). But if you'd like it to, then yes, reach out to support and ask for it. $\endgroup$Around
by a number is documented but still produces incorrect result. $\endgroup$-Around[-1, {0.5, 1.5}]
has similar problems. The behavior ofAbout
seems consistent withf[About[x, {a,b}]]
beingAbout[f[x], {Abs[f'[x]]*a, Abs[f'[x]]*b}]
. $\endgroup$