[GiNaC-list] unevaluated add in the result of imag_form()

[Richard B. Kreckel]

Hi!

Burcin Erocal wrote:
> While looking into a problem in numerical evaluation in pynac, I ran
> into the following:
> 
> ginsh - GiNaC Interactive Shell (ginac V1.5.7)
> <snip>
> Type ?? for a list of help topics.
>> a=(sqrt(4*(sqrt(3) - 5)*(sqrt(3) + 5) + 48) + 4*sqrt(3))/ (sqrt(3) +
>> 5);
> (sqrt(48+4*(5+sqrt(3))*(-5+sqrt(3)))+4*sqrt(3))*(5+sqrt(3))^(-1)
>> imag_part(a);
> (5+sqrt(3))^(-1)*sqrt(abs(48+4*(5+sqrt(3))*(-5+sqrt(3))))*sin(1/2*atan2(0,48+4*(-22)))
> 
> Note that the second argument of atan2 is an add object in a rather
> unusual form: 48+4*(-22)
> 
> Is this intended behavior?

Definitely not. A simpler case exhibiting the same problem is 
real_part(1+2*(sqrt(2)+1)*(sqrt(2)-1)).

It seems to me that add::eval() is a little bit too simple-minded: 
add::real_part() returns an add with overall_coeff 1 and an expair with 
rest 1 and coeff 2, i.e. 1+2*1, but there is no case in add::eval() to 
take care of this.

Bye,
   -richy.
-- 
Richard B. Kreckel
<http://www.ginac.de/~kreckel/>