Out of range floating point number determination

On 8/12/2012 4:11 PM, Robert Dodier wrote:
> On 2012-08-11, Edward A Romana <erom at earthlink.net> wrote:
>
>>  From the Maxima level, I would like to determine when evaluation of a
>> floating point expression is out of range.
> The Common Lisp standard does not allow for non-numerical float values
> such as infinity, negative infinity, and not-a-number.
Eh, I think it allows them but does not require them.
>   So any having to
> do with such floats is implementation-dependent.
This is not actually necessary to help Edward.
There is a standard suite of stuff for handling errors in Lisp:

(defun ten2p (p) (handler-case (expt 10.0 p) (arithmetic-error (v) 'und)))

computes 10.0^p.   When this causes an error, it returns the symbol 'und.

You can read all about it in the common lisp documentation online.
 From the Maxima top level this would not, I think, be something you can 
utter.

However a little bit of lisp should work if you can avoid evaluation and 
then do it later.
There is an mfexpr* property or something like that which can be used.  
I haven't debugged it but
maybe
(defprop $catcharith (lambda(x)(handler-case (meval x) 
(arithmetic-error(v) '$und))) mfexpr*)

then at maxima top level

(%i10)    catcharith(10.0^319);
might return und.

except I haven't tried this, and I am unsure about the mfexpr*

RJF

>   Some implementations
> allow such values, some don't. Clisp doesn't, SBCL does; I don't
> remember about any others.
>
> I wonder what is your larger goal here. If you are trying to avoid
> float(x) where x is too big so it causes an error, my advice is to
> switch to an implementation, such as SBCL, which allows non-numerical
> floats.
Producing an NaN and passing it around within Maxma is not necessarily 
going to work.

>   That might obviate the need for such logic in your own code.
>
>> I had no luck finding   i.nf*10^0   in the documentation.
> It is probably a messed-up version of an implementation-dependent name
> for float infinity. I suppose that's a bug in EXPLODEN (function to
> format numbers for display).
yep.
>
> Hope this helps,
>
> Robert Dodier
>
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