strange behaviour with simple decimals



Stavros Macrakis wrote:
> On 4/13/07, *Raymond Toy* <toy.raymond at gmail.com
> <mailto:toy.raymond at gmail.com>> wrote:
>
>     Jay Belanger wrote:
>     > Raymond Toy <toy.raymond at gmail.com
>     <mailto:toy.raymond at gmail.com>> writes:
>     >> I also don't understand why the defaults for maxima should
>     cater to the
>     >> least experienced and knowledgeable users.
>     >
>     > Because they're the ones we want to start using Maxima, because
>     > they're the ones who are least able to change the defaults ...
>     >
>     Except that they're only a beginner once.  Tell them how to change
>     it,
>     point out the numerous web pages that explain floating-point
>     etc.   Once
>     they're past that stage, the defaults may be annoying.
>
>
> Yes, they are only a beginner once.  Once they are no longer
> beginners, they can edit their init files etc.  (Though actually it
> would be nicer if we could provide a way *within Maxima* to change
> defaults, e.g. set_init(fpprintprec,6) )
What do you mean by this?  Does set_init modify an init file to set the
given parameter to the given value?


>
> Actually, I think that understanding floating point etc. comes long
> after understanding basic algebra.  A beginner in algebra (9th grade,
> say), can understand factor(x^3-1) and bfloat(%pi),fpprec:100 and
> trigsimp(sin(x)^2-cos(x)^2), but I wouldn't expect him or her to
> understand rounding and cancellation errors.
>
>  
Yes, you're probably right.  But I think a 9th grader that could
understand those operations would be able to understand rounding and
cancellation.  My 4th grade kid has already learned about rounding.  A
few examples about cancellation should enlighten a 9th grader.

But I must confess that I don't really use maxima for anything other
than a glorified calculator and grapher.   I guess my preferences might
differ wildly from someone who actually uses maxima to do interesting stuff.

Ray