OpenEuphoria

Re: Current implementation of exp() is faulty.

• Posted by Matt Lewis <matthewwalkerlewis at gma?l?com> May 09, 2008
• 771 views

CChris wrote:
> 
> }}}
<eucode>
> include machine.e
> include math.e
> ?atom_to_float64(power(E,20.0))
> ?atom_to_float64
>
> (485165195.409790277969106830541540558684638988944847254353610800315977996142709740165979850652747349447833789438961)
> ?atom_to_float64(power(E,12.0))
> ?atom_to_float64(
>
> 162754.7914190039208080052048984867831702092844787207704435562481385967708355437387292882419094316843)
> ?atom_to_float64(power(E,10.0))
> ?atom_to_float64(
>
> 22026.46579480671651695790064528424436635351261855678107423542635522520281857079257519912096816452590)
> ?atom_to_float64(power(E,8.0))
> ?atom_to_float64(
>
> 2980.957987041728274743592099452888673755967939132835702208963530387730725173367530157371871490018139)
> ?atom_to_float64(power(E,6.0))
> ?atom_to_float64(
>
> 403.4287934927351226083871805433882796058998973571292026139671883251511806339934983051788866512126648)
> ?atom_to_float64(power(E,5.0))
> ?atom_to_float64(
>
> 148.4131591025766034211155800405522796234876675938789890467528451109120648209585760796884094598990211)
> ?machine_func(26,0)
> </eucode>
{{{

> 
> Results:
> {253,231,104,139,8,235,188,65}
> {3,232,104,139,8,235,188,65}
> {152,124,211,84,22,222,3,65}
> {154,124,211,84,22,222,3,65}
> {93,5,149,207,157,130,213,64}
> {97,5,149,207,157,130,213,64}
> {108,12,71,125,234,73,167,64}
> {110,12,71,125,234,73,167,64}
> {141,192,144,86,220,54,121,64}
> {142,192,144,86,220,54,121,64}
> {142,51,112,153,56,141,98,64}
> {142,51,112,153,56,141,98,64}
> 
> 
> So, discrepancies start showing up for values of the argument as small as 6,
> or even smaller.

Are you certain that it's the implementation of exp and not the parsing 
of floating point?  You're way beyond the precision that the current
floating point scanner can handle.  Try changing to scientific notation.
I just added E+0 to all of your ridiculously precise numbers, and here's
what I got:

{251,231,104,139,8,235,188,65}
{4,232,104,139,8,235,188,65}
{151,124,211,84,22,222,3,65}
{154,124,211,84,22,222,3,65}
{92,5,149,207,157,130,213,64}
{96,5,149,207,157,130,213,64}
{107,12,71,125,234,73,167,64}
{110,12,71,125,234,73,167,64}
{141,192,144,86,220,54,121,64}
{143,192,144,86,220,54,121,64}
{142,51,112,153,56,141,98,64}
{143,51,112,153,56,141,98,64}


Frankly, I have idea how close to Mathematica's result these are.  You
never told us what those answers were.

Matt