Status: Accepted
Owner: [email protected]
Labels: Type-Defect Priority-Medium
New issue 2236 by [email protected]: solve fails for polysys with multiple
solutions
http://code.google.com/p/sympy/issues/detail?id=2236
Here is the original problem:
>>> var('lam a0 conc')
(lam, a0, conc)
>>> eqs = [lam+2*y-a0*(1 - x/2)*x-0.005*x/2*x, a0*(1 - x/
... 2)*x-1*y-0.743436700916726*y, x+y-conc]
>>> sym=[x,y,a0]
>>> solve(eqs, sym)
Traceback (most recent call last):
...
sympy.polys.polyerrors.DomainError: can't compute a Groebner basis over
RR
So the reals present a problem. Change them to rationals:
>>> reqs=[nsimplify(e,rational=True) for e in eqs]
>>> solve(reqs, sym)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "sympy\solvers\solvers.py", line 385, in solve
soln = solve_poly_system(polys)
File "sympy\solvers\polysys.py", line 45, in solve_poly_system
return solve_generic(polys, opt)
File "sympy\solvers\polysys.py", line 179, in solve_generic
result = solve_reduced_system(polys, opt.gens, entry=True)
File "sympy\solvers\polysys.py", line 149, in solve_reduced_system
raise NotImplementedError("only zero-dimensional systems supported
(finite n
umber of solutions)")
NotImplementedError: only zero-dimensional systems supported (finite
number of s
olutions)
Try solve this by hand:
>>> yy = solve(reqs[0],y)[0]
>>> a00 = solve(reqs[1].subs(y,yy),a0)[0]
>>> xx = solve(reqs[2].subs(((y,yy), (a0,a00)),x)
>>> len(xx)
2
So the problem appears to be that there are two solutions? The error
message mentions finite number of solutions. Does it really mean that there
should be a single solution?
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