[GiNaC-list] Internal error: statement in file ./real/conv/cl_R_to_double.cc, line 55 has been reached!!

[Sheplyakov Alexei]

Hello!

On Fri, Dec 08, 2006 at 12:14:42PM +0000, Pedro Cruz wrote:
> Hi,
> 
> --------------------
> this output
> --------------------
> 
> Pi=3.1415926535897932385
> Internal error: statement in file ./real/conv/cl_R_to_double.cc, line 55
> has been reached!!
> Please send the authors of the program a description how you produced
> this error!
> 
> --------------------
> has been produced by 
> --------------------
> 
> 
> #include <iostream>
> #include <sstream>
> #include <stdexcept>
> #include <ginac/ginac.h>
> using namespace std;
> using namespace GiNaC;
> 
> 
> int main()
> {
>   cout << "Pi=" << Pi.evalf() << endl;
> 
>   if (is_a<constant>(Pi)) {
>     double f = ex_to<numeric>(Pi).to_double();
>     cout << f << endl;
>   }
> 
>   return 0;
> }

ex_to is unsafe function (this is documented in the manual), so you
should check if the expression in question is really of type T before
converting it with ex_to<T> (unless you *really* know what are you doing).
Pi is not numeric, but a contstant, so your code is expected to fail.

> ---------------------------------------------
> on debian (etch testing) with libginac1.3c2a.
> ---------------------------------------------
> 
> It was a first example i tried to do
> in order to understand ginac/cln concepts:
> <ex>
> <constant> and
> <numeric>.
> 
 
> How to convert from Pi to C++ double type in one C++ line ?

Quoting the manual:

"GiNaC keeps algebraic expressions, numbers and constants in their exact
form. To evaluate them using floating-point arithmetics you need to call

ex ex::evalf(int level = 0) const;"

So, use something like this:

double f = ex_to<numeric>(Pi.evalf()).to_double();

Also you could try this patch:
http://www.ginac.de/pipermail/ginac-list/2006-October/000993.html

Using this patch the same code can be written as:

double f;
numconv_to(Pi, f);

Best regards,
 Alexei


-- 
All science is either physics or stamp collecting.

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