Hello,
I'm afraid the logic of this is still beyond me (yes, it might be my
mathematical ignorance).
I created a class ncsymbol derived from basic (by copying the GinaC
symbol class and overloading return_type())
Now I have the following test program
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#include <ginac/ginac.h>
#include "ncsymbol.h"
using namespace GiNaC;
int main() {
ncsymbol s1("s1", "s1");
symbol x("x"), y("y");
matrix M1(2,2);
M1 = x, 0, y, 0;
matrix M2(2,2);
M2 = 0, x, x, 0;
ncsymbol s2("s2");
ex nc;
nc = s1 * s2; // Produces a ncmul
nc = nc.subs(s1 == M1); // Produces a mul !!
nc = M2 * M3; // Produces a ncmul
nc = s1 * M2; // Produces a mul !!
}
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1. Why does replacing a non-commutative object with another
non-commutative object result in the ncmul becoming a mul?
2. Why is the product of two (different) non-commutative objects a mul
and not a ncmul?
Thanks for any light,
Jan