I have found that the quartics routine can return two sets of 4 roots
(that can be selected by exchanging the signs in A and B of the
routine). The present set returned is correct if there are 4 real
roots or if there are 2 real and all the coefficients are real. The
other set (according to the tests that I have done so far) is needed
for all other cases.
This poses a problem that I am interested in getting some opinions:
1) to maintain backward compatibility I can make the arguments be (f,
sign=-1) but is that
wise? One really should be selecting which set is desired.
2) If the number of real roots can't be determined then I should send
back the solution set with a symbol replacing the sign. Perhaps this
is the answer to (1), too: if no sign is specified then send back a
solution set with a symbol for the sign. If the user had sent a
polynomial for which the number of real roots could be determined,
then the sign will be known. But if they don't they will get an answer
with a new symbol in it for the sign. The question is, what type of
symbol should be used, and what would be a good name (sign,
sign_1_if_cmplx_roots_neg1_if_all_real, ...)? If I use a regular
symbol the user can access it in the sending code but there might be a
conflict with the user's symbols. That can be avoided by using a dummy
symbol, but then how will the user do a subs() to specify the sign?
###
>>> def test(a,b):
... return a+Symbol('s',dummy=True)*b, a+Symbol('s')*b
...
>>> f1, f2 = test(1,2); f1, f2
(1 + 2*_s, 1 + 2*s)
>>> f2.subs(s,1)
3
>>> f1.subs(Symbol('_s'),1) #how do I replace the dummy with 1?
1 + 2*_s
>>>
>>> f1, f2 = test(s,2); f1, f2 #conflicting variable 's' combines with the one
>>> in test()
(s + 2*_s, 3*s)
###
/c
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"sympy" group.
To post to this group, send email to sympy@googlegroups.com
To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com
For more options, visit this group at http://groups.google.com/group/sympy?hl=en
-~----------~----~----~----~------~----~------~--~---
