Accuracy and error analysis (was Re: [Maxima] primes)



--- Robert Dodier  wrote:

> > With a full set of pre-processing / post-processing hooks
> > analogous to Mma's $PreRead, $Pre, $PrePrint, $Post, one 
> > can then easily arrange for with_error_analysis() to be
> > wrapped around every expression if this is desired.
> 
> I'm afraid this makes me rather nervous. I don't think
> global hooks are necessary for implementing error analysis,
> and they bring the potential for just the kind of rippling
> effects that I'd like to avoid.

No need to be nervous about the mechanisms, as such - it's the
application of them that is occasionally tricky, and that is up to the
user/programmer.  The mechanisms are totally dormant until someone
deliberately starts playing with them.  With post_eval_functions, I
once or twice inadvertantly programmed in something that caused a
looping situation, for example.  But used properly, it makes unit
simplification operate automatically and very smoothly.  Think of
having pre/post processing hooks as having steak knives available in
the kitchen - you sometimes need 'em to slice up a steak, but you don't
use them when eating a regular meal.

CY

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