Brian Blais wrote:
Hello,
I wrote a very simple script using sympy, and things were working fine,
except for one problem. So I have:
You will probably want to ask on the sympy mailing list:
http://groups.google.com/group/sympy
from sympy import *
x, y = symbols('x','y',real=True)
alpha,beta,gamma=symbols('alpha','beta','gamma',real=True)
alpha_p,beta_p,gamma_p=symbols('alpha_p','beta_p','gamma_p',real=True)
L = symbols('L',real=True)
and then I look at solutions to some equations, like:
solution=solve([beta*y - alpha*(1+y/L) ,
-beta_p*x + alpha_p ], [x, y])
print solution
which prints (correctly):
{x: alpha_p/beta_p, y: L*alpha/(-alpha + L*beta)}
now, if I do:
solution=solve([beta*y - alpha*(1+y/L) - gamma*x*(1+y/L),
-beta_p*x + alpha_p - gamma_p*y], [x, y])
print solution
I get a very long solution, which isn't a problem, but it isn't a
dictionary: I can't tell what is the solution for x and for y. What I
get is:
[(-(alpha*beta_p*abs(gamma)*abs(gamma_p) +
alpha_p*gamma*abs(gamma)*abs(gamma_p) -
L*beta*beta_p*abs(gamma)*abs(gamma_p) -
L*gamma*gamma_p*abs(gamma)*abs(gamma_p) -
gamma*gamma_p*(2*alpha*alpha_p*beta_p*gamma -
2*L*alpha_p*beta*beta_p*gamma + 2*L*alpha*beta_p*gamma*gamma_p +
alpha**2*beta_p**2 + alpha_p**2*gamma**2 + L**2*beta**2*beta_p**2 +
L**2*gamma**2*gamma_p**2 - 2*L*alpha*beta*beta_p**2 +
2*L*alpha_p*gamma_p*gamma**2 +
2*beta*beta_p*gamma*gamma_p*L**2)**(1/2))/(2*beta_p*gamma*abs(gamma)*abs(gamma_p))
+ alpha_p/beta_p, (alpha*beta_p*abs(gamma)*abs(gamma_p) +
alpha_p*gamma*abs(gamma)*abs(gamma_p) -
L*beta*beta_p*abs(gamma)*abs(gamma_p) -
L*gamma*gamma_p*abs(gamma)*abs(gamma_p) -
gamma*gamma_p*(2*alpha*alpha_p*beta_p*gamma -
2*L*alpha_p*beta*beta_p*gamma + 2*L*alpha*beta_p*gamma*gamma_p +
alpha**2*beta_p**2 + alpha_p**2*gamma**2 + L**2*beta**2*beta_p**2 +
L**2*gamma**2*gamma_p**2 - 2*L*alpha*beta*beta_p**2 +
2*L*alpha_p*gamma_p*gamma**2 +
2*beta*beta_p*gamma*gamma_p*L**2)**(1/2))/(2*gamma*gamma_p*abs(gamma)*abs(gamma_p))),
(-(alpha*beta_p*abs(gamma)*abs(gamma_p) +
alpha_p*gamma*abs(gamma)*abs(gamma_p) -
L*beta*beta_p*abs(gamma)*abs(gamma_p) -
L*gamma*gamma_p*abs(gamma)*abs(gamma_p) +
gamma*gamma_p*(2*alpha*alpha_p*beta_p*gamma -
2*L*alpha_p*beta*beta_p*gamma + 2*L*alpha*beta_p*gamma*gamma_p +
alpha**2*beta_p**2 + alpha_p**2*gamma**2 + L**2*beta**2*beta_p**2 +
L**2*gamma**2*gamma_p**2 - 2*L*alpha*beta*beta_p**2 +
2*L*alpha_p*gamma_p*gamma**2 +
2*beta*beta_p*gamma*gamma_p*L**2)**(1/2))/(2*beta_p*gamma*abs(gamma)*abs(gamma_p))
+ alpha_p/beta_p, (alpha*beta_p*abs(gamma)*abs(gamma_p) +
alpha_p*gamma*abs(gamma)*abs(gamma_p) -
L*beta*beta_p*abs(gamma)*abs(gamma_p) -
L*gamma*gamma_p*abs(gamma)*abs(gamma_p) +
gamma*gamma_p*(2*alpha*alpha_p*beta_p*gamma -
2*L*alpha_p*beta*beta_p*gamma + 2*L*alpha*beta_p*gamma*gamma_p +
alpha**2*beta_p**2 + alpha_p**2*gamma**2 + L**2*beta**2*beta_p**2 +
L**2*gamma**2*gamma_p**2 - 2*L*alpha*beta*beta_p**2 +
2*L*alpha_p*gamma_p*gamma**2 +
2*beta*beta_p*gamma*gamma_p*L**2)**(1/2))/(2*gamma*gamma_p*abs(gamma)*abs(gamma_p)))]
which, if you ignore the complexity, is a list of two items, each item
is a tuple of length 2. What does this mean? I can handle the mess of
the solution, but I'd like to know what is a solution for x, and for y.
Why isn't it in a dictionary? Am I doing something wrong?
I suspect that the latter are two possible solutions given as an (x,y) pair.
Possibly, they should be given as a list of dicts. Ask on the sympy mailing list.
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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