expr.poly(x) does not really make expr a polynomial in x, it's a quite useless method. If you give no parameter to ex.coefficients() it takes the lexicographically first variable. So instead of ex.poly(x).coefficients do ex.coefficients(x), and you get:
sage: (zeta*diff(f(tau), tau)).coefficients(tau) [[zeta*diff(f(tau), tau), 0]] sage: (zeta*diff(f(tau), tau)).coefficients(zeta) [[diff(f(tau), tau), 1]] sage: (a*diff(f(b), b)).coefficients(a) [[diff(f(b), b), 1]] sage: (a*diff(f(b), b)).coefficients(b) [[a*diff(f(b), b), 0]] Regards, -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
