I think you have more chances if you work in QQ['a']['t1,t2']. In any case, it seems that it is better to convert to your ring using P(f.polynomial(QQ)) than performing substitutions.
sage: K=QQ['a']['t1,t2'] sage: K1=SR['t1,t2'] sage: f=SR(K.random_element(100,500)).expand() sage: %time g=K(f.polynomial(QQ)) CPU times: user 0.06 s, sys: 0.00 s, total: 0.06 s Wall time: 0.06 s sage: %time g=K1(f.polynomial(QQ)) CPU times: user 0.11 s, sys: 0.00 s, total: 0.11 s Wall time: 0.11 s sage: t1,t2=K1.gens() sage: %time g=f.polynomial(QQ)(t1=t1,t2=t2) CPU times: user 2.52 s, sys: 0.02 s, total: 2.53 s Wall time: 2.51 s -- You received this message because you are subscribed to the Google Groups "sage-support" 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 http://groups.google.com/group/sage-support?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
