Exponentiation used in division? & Some extrordinary slowness is some problems.

I wanted to keep the option of using bfloats open; I think I cannot do 
that with modedeclare. At any rate that
is what I remember - am I wrong? I don't doubt modedeclare would speed 
it up. Still the discrepancy in time
for those two problems seems awfully great, even just compared to other 
of my maxima code. If noone wants to look at it, that is fine. I just 
thought it might help too know.

Dennis Darland
student at dennisdarland.com

On 12/31/2013 8:39 AM, Richard Fateman wrote:
> On 12/31/2013 12:57 AM, Dennis Darland - student wrote:
>> Exponentiation is very inefficient compared to division!
>> Why is it used here in maxima? (or appear to be)
> very inefficient??
>
> a/b  is  a* b^(-1) by definition.   b^(-1)  is the same as 1/b. One 
> division.
> Then a* (1/b)  is one multiplication.
>
> The advantage of treating a/b as a*b^(-1)  is that one only has one 
> case to worry about,
> whether it was written as a/b  or   a*b^n  with n=-1.
>
>
>> Example:
>> ------------------------------------------------------------------------------------ 
>>
>> Maxima 5.30.0 http://maxima.sourceforge.net
>> using Lisp GNU Common Lisp (GCL) GCL 2.6.8 (a.k.a. GCL)
>> Distributed under the GNU Public License. See the file COPYING.
>> Dedicated to the memory of William Schelter.
>> The function bug_report() provides bug reporting information.
>> (%i1) (4.0/0.0);
>> expt: undefined: 0 to a negative exponent.
>>  -- an error. To debug this try: debugmode(true);
>> (%i2)
>> ------------------------------------------------------------------------------------------------ 
>>
>> I do not expect maxima to be comparable to c at number crunching,
>> but there are two examples in my tests that it appears would take over
>> one day to complete using maxima, but take only 4 and 5 seconds
>> respectively in c.
> You are probably not using Maxima in its most efficient way.
>> Most of my tests take under one minute even in maxima.
>> The algorithms are the same for maxima and c.
> Maxima is probably doing something much more generally than necessary.
>
>> As I don't know the internals of maxima, I cannot tackle it. Perhaps it
>> is worth someones time to look into. I wouldn't be surprised if it were
>> related to the problem above, but do not know.
> This is unlikely, since it probably would not happen if it were 
> compiled with proper declarations
> and compilation
>
>> My test results and source code are at:
>> http://sode.sourceforge.net/
>
> /You will have to be WAY more specific if you want someone to look at 
> some specific source code.
>
> A simple question:  have you used modedeclare and compile  in Maxima?
> Where in your code exactly?
>
> RJF
>
> /
>> ------------------------------------------------------------------------------------------------------ 
>>
>>
>>
>> Dennis Darland
>> student at dennisdarland.com
>>
>> _______________________________________________
>> Maxima mailing list
>> Maxima at math.utexas.edu
>> http://www.math.utexas.edu/mailman/listinfo/maxima
>