Re: [asa] Creation Care

--- Dave Wallace <wdwllace@sympatico.ca> wrote:

> Does anybody on the list know if the results taken from the climate
> modeling systems are essentially at the strange attractor limit cycle or
> are the results taken from a much earlier point when the behavior has
> not settled down into a limit cycle?
>
I'm not familiar with the models, but I've read the literature on chaotic
systems, including the Lorentz attractor, which is intended to be a model for
weather. I would say that if the climatic models do not take the chaotic
nature of weather into account, they will give erroneous results.
 
> >
> > Very large software systems are usually designed in modules that can
> > each be unit-tested, but it's clear that you won't track down all the
> > bugs. However, testing against historical data is probably a pretty
> > good test of the correctness of the algorithm - most bugs would cause
> > the system to give nonsensical results.
>
> I understand that programs are broken up into modules (classes) in a
> divide and conquer strategy to try to manage the intellectual complexity
> and that these should be unit tested. However unit testing often is not
> done as well as it should be even by graduates with computer degrees.
> Specifying the contract that the module is supposed to meet is extremely
> hard, especially for error conditions but also for what is legal usage
> of a complex higher level module that in turn depends on other modules.

AQnd when you connect the modules together you could be unfortunate enough to
have created a chaotic system. I developed embedded software for the automotive
industry for the last 23 years of my career. We specified each module
carefully, specified all the interactions and did extensive unit testing. But
in road testing -- which was always quite extensive -- we always discovered
situations that hadn't occurred to us. Our specifications and architecture were
good enough that it was usually not too difficult to incorporate checks and
actions for these situations, but I wouldn't trust any software that hasn't
been tested extensively, against real data.
>
> I spent about 25 years of my career involved with compiler development
> including state of the art optimizers. For none specialists, compilers
> are large complex programs that translate computer languages into
> something that a machine can execute. Because climate models are
> typically compute intensive, some kind of optimizer would be used to
> improve the efficiency of the running code. The optimizer programming
> teams knew the computer language rules very well and very frequently
> they would get bug reports that when examined would turn out that the
> programmer submitting the bug, had not followed the language rules. In
> some cases the language rule that was broken was subtle but in other
> cases the programmers were egregiously in violation of the language
> standard. Of course the optimizers and related tools that adapt for
> running on parallel machines also have bugs, much to the development
> teams chagrin. Every valid bug found usually become part of our test
> suite but there is always one more...
>
> Dave Wallace
>
>
> To unsubscribe, send a message to majordomo@calvin.edu with
> "unsubscribe asa" (no quotes) as the body of the message.
>

Bill Hamilton
William E. Hamilton, Jr., Ph.D.
248.652.4148 (home) 248.821.8156 (mobile)
"...If God is for us, who is against us?" Rom 8:31

 
____________________________________________________________________________________
Sucker-punch spam with award-winning protection.
Try the free Yahoo! Mail Beta.
http://advision.webevents.yahoo.com/mailbeta/features_spam.html

To unsubscribe, send a message to majordomo@calvin.edu with
"unsubscribe asa" (no quotes) as the body of the message.
Received on Sun Jan 21 19:04:56 2007