problems with interval arithmetic
- To: mathgroup at yoda.physics.unc.edu
- Subject: problems with interval arithmetic
- From: fred at mi.el.utwente.nl (Fred Hugen - UT)
- Date: Mon, 25 Oct 93 10:04:22 +0100
Hello,
I worked for while with interval arithmetic under Mma version 2.2.1 and
encountered something strange. Using constants within builIn mathematical
functions, such as Cos[Pi/2] and Sqrt[2], gives (completely) other results in
contrast to using the numerical approximations of these constants.
The following fragment shows this strange behaviour:
In[1] := exp1 = (x / Sqrt[2]) - (y / Sqrt[2]);
N[exp1] /. {x->Interval[{16,20}], y-> Interval[{16,20}]}
N[exp1 /. {x-> Interval[{16,20}] , y -> Interval[{16,20}]}]
Out[1] := Interval[{-2.82843, 2.82843}]
Interval[{22.6274, 28.2843}]
The first result seems to be the correct one. I can't explane the second.
Has it to with the representation of Sqrt[2]?
Has anyone an explanation, or is it a bug?
(I send the same message to WRI).
Thanks anyway,
Fred Hugen