[Maxima] find_root error

Raymond Toy (RT/EUS) raymond.toy at ericsson.com
Tue Jul 22 08:55:11 CDT 2008


Stavros Macrakis wrote:
> Thanks for the bug report. Sorry Maxima gets the wrong answer here.
> 
> I'm pretty sure that the problem is that Maxima simplifies (655/656)^n 
> -> 655^n/656^n (which is correct), then tries to evaluate that 
> expression for various float values of n. For n>109 or so, the 
> intermediate values are IEEE Inf's, and so the quotient is an IEEE NaN.  
> Unfortunately, Maxima doesn't know how to handle IEEE Inf/NaN, and even 
> worse, does not signal an error to indicate this.

Perhaps this is a gcl problem?  Both clisp and cmucl return the noun 
form, with no indication of overflow or invalid operation or anything.

Ray

> 
> It is also embarrassing that Maxima can't solve (655/656)^n=1/2 
> symbolically.
> 
> Could you please submit this bug to our bug tracking system?  (Use 
> bug_report()$ for instructions.)
> 
> Thanks,
> 
>                 -s
> 
> On Tue, Jul 22, 2008 at 8:30 AM, Tawny Owl <tow_force at hotmail.com 
> <mailto:tow_force at hotmail.com>> wrote:
> 
>     I am using Maxima 5.15.0 under Windows.
>      
>     find_root((655/656)^n = 0.5, n, 1, 1000) gives 114.8, which is
>     completely wrong.
>      
>     Fortunately, I checked the answer (always a good habit, I know!).
>      
>     Either of the following expressions give the correct answer, which
>     is 454.4
>      
>     find_root(float(655/656)^n = 0.5, n, 1, 1000);
>     float(log(0.5)/log(655/656));
> 
>     ------------------------------------------------------------------------
>     Get fish-slapping on Messenger! Play Now
>     <http://clk.atdmt.com/UKM/go/101719805/direct/01/>
> 
>     _______________________________________________
>     Maxima mailing list
>     Maxima at math.utexas.edu <mailto:Maxima at math.utexas.edu>
>     http://www.math.utexas.edu/mailman/listinfo/maxima
> 
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> Maxima mailing list
> Maxima at math.utexas.edu
> http://www.math.utexas.edu/mailman/listinfo/maxima


More information about the Maxima mailing list