From: "Alxneit-Kamber Ivo" <ivo.alxneit@psi.ch>
To: <gsl-discuss@sources.redhat.com>
Subject: possible design weekness
Date: Fri, 09 Mar 2007 13:58:00 -0000 [thread overview]
Message-ID: <1173448719.10868.3.camel@pc446.psi.ch> (raw)
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Dear all
I have recently been bitten by what seems to be a design weekness in how
the functions (function to be minimized, or system of ODE's) are
defined. These function do not return a status value but the function
value. This prevents to easily notifiy the caller (iterate) of a failure
such as e.g. a domain error of one of its arguments or a failed
malloc().
The function used in the non-linear least squares fit, however is
implemented better as it returns a status value to the caller. Other
parts of the GSL library, multi-dimensional root finding or
one-dimensional minimization, e.g., take a slightly less optimal
aprroach. Here the caller (iterate) checks, if the function value or its
derivative, if applicable, is finite and issues an error otherwise.
I think it would be worthwhile (maybe for a version 2.0) to implement
a common definition for these functions like
status = f(double *result, 'arguments', (void*) parameters);
For a status different from 'GSL_SUCCESS' let the driver either take
care of the failure (this depends on the application/algorithm) or let
it fail propagating the status from the function to the user. Then the
user can handle the situation in his main loop.
I currently have no real idea how to prevent breaking of old user code
by implementing this new interface while keeping the old in place:
- for the 'GSL_XXX_EVAL_YYY' family of macros a simple wrapper would
do the job. (allways return GSL_SUCCESS for the old style or analyze
the result and then assign the status to be returned).
- the fact that the new interface has one more argument could probably
be handled by variable argument functions (never used these).
- how to deal with the fact that the new style function is of different
type (int instead of double)?
Comments or suggestions?
--
Dr. Ivo Alxneit
Laboratory for Solar Technology phone: +41 56 310 4092
Paul Scherrer Institute fax: +41 56 310 2688
CH-5232 Villigen http://solar.web.psi.ch
Switzerland gnupg key: 0x515E30C7
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next reply other threads:[~2007-03-09 13:58 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-09 13:58 Alxneit-Kamber Ivo [this message]
2007-03-12 21:26 ` Brian Gough
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