[GiNaC-devel] removing the evil

[Richard B. Kreckel]

Dear Alexei,

I wrote:
> Alexei Sheplyakov wrote:
>> 2. (a consequence of 1) No bugs like this:
>>
>> ex e1, e2; 
>> // do some calculation
>> if (e1 == e2) { // gotcha: this is always true.
>> 	// do something
>> }
> 
> Well, over here I get:
> 
> $ cat relationaltest.cc
> #include <iostream>
> #include <ginac/ginac.h>
> using namespace std;
> using namespace GiNaC;
> 
> int main()
> {
>      symbol x("x");
>      ex e1, e2;
>      // do some calculation
>      e1 = series(tgamma(x),x==0,3).op(3);
>      e2 = series(log(x),x==1,6).op(4);
>      cout << e1 << endl;
>      cout << e2 << endl;
>      if (e1 == e2) { // gotcha: what happens?
>          cout << "e1 and e2 appear to be equal." << endl;
>      } else {
>          cout << "e1 and e2 appear to differ." << endl;
>      }
> }
> $ g++ -O relationaltest.cc -lginac
> $ ./a.out
> -1/12*x^2*(2*Euler^3+Euler*Pi^2+4*zeta(3))
> 1/5*(-1+x)^5
> e1 and e2 appear to differ.
> 
> What is your point?

I'm reading my batch of email backwards. I've now seen 
<http://www.ginac.de/pipermail/ginac-devel/2008-July/001370.html>, but 
when I try to complete these examples, they don't work as you describe:

$ cat relationaltest1.cc
#include <iostream>
#include <ginac/ginac.h>
using namespace std;
using namespace GiNaC;

int main()
{
     unsigned n = 2;
     symbol A("A");
     symbol mu_sym("mu");
     idx mu(mu_sym,4);
     if (n == ex_to<idx>(mu).get_dim()) {
         cout << "doing something" << endl;
     } else {
         cout << "doing nothing" << endl;
     }
}
$ g++ -O relationaltest1.cc -lginac
$ ./a.out
doing nothing
$ cat relationaltest2.cc
#include <iostream>
#include <ginac/ginac.h>
using namespace std;
using namespace GiNaC;

int main()
{
     matrix M(4,4);
     for (unsigned r=0; r<4; ++r) {
         for (unsigned c=0; c<4; ++c) {
             M.set(r,c,numeric(1,r+c+1));
         }
     }
     if (M(1,2) != M(2,1)) {
         cout << "M(1,2) and M(2,1) appear to differ." << endl;
     } else {
         cout << "M(1,2) and M(2,1) appear to be equal." << endl;
     }
     if (M(1,3) != M(0,0)) {
         cout << "M(1,3) and M(0,0) appear to differ." << endl;
     } else {
         cout << "M(1,3) and M(0,0) appear to be equal." << endl;
     }
}
$ g++ -O relationaltest2.cc -lginac
$ ./a.out
M(1,2) and M(2,1) appear to be equal.
M(1,3) and M(0,0) appear to differ.

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