[std-interval] discontinuity flag
Prof.Dr.J.Wolff von Gudenberg
wolff at informatik.uni-wuerzburg.de
Thu Oct 5 14:41:01 PDT 2006
a short notice to clarify defintion and use of the discontinuity flag
>>> The discussion showed that Standard functions MUST set a flag when
>>> the argument interval is not completely contained in the domain of
>>> the function. Otherwise (i.e without the flag) verification of the
>>> result with fixed points or other assertions that need continuity is
>>> not possible
Our proposal is a flag as u user defined boolean variable, so not a
global (hardware) flag.
standard functions come with 2 interfaces, one completely ignoring the
flag and one that sets it in case of discontinuity or being undefined
John's description of context
4. Hence the typical pattern of use is
- The DESOLVE manual tells the Engineer how to implement APPFCN, including
to do so without clearing the DISCONT flag.
At run time
- Trusted Code DESOLVE clears the DISCONT flag.
- DESOLVE calls Untrusted Code APPFCN.
- On return DESOLVE inspects the flag. If it remains un-set, and APPFCN is
written correctly, the Brouwer conditions have been rigorously verified.
clearly describes the scenario
and the engineer has to rewrite his source code anyhow if it is applied
in the context of a new (interval) solver
Another point: We are afraid of delegating some of the behavior
(semantics) to the compiler. Experience with compilers has shown that
they usually do not understand the proper handling of arithmetic flags
or settings, see the switching of the rounding mode, e.g.
Prof. Dr. Juergen Wolff v. Gudenberg <wolff at informatik.uni-wuerzburg.de>
o Lehrstuhl fuer Informatik II
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