SympifyError解析多項式

Question

私は多項式関数を書いたPythonプログラムを持っており、Sympyのsolve()関数を使ってその逆を見つける。私は次のエラーを取得するプログラムの実行時に

x = Symbol('x') 
y = Symbol('y') 
for i in range(10): 
    p = Poly.create_random() 
    print("p orig " + str(p)) 
    solve(p, x) 
    print("p in terms of x: " + str(p)) 
    solve(p, y) 
    print("p in terms of y (inverse): " + str(p)) 

しかし、：Sympyについては

p orig y = 5*x**2 - 55*x**1 + 140 
Traceback (most recent call last): 
    File "/usr/local/lib/python3.5/dist-packages/sympy/core/sympify.py", line 354, in sympify 
    expr = parse_expr(a, local_dict=locals, transformations=transformations, evaluate=evaluate) 
    File "/usr/local/lib/python3.5/dist-packages/sympy/parsing/sympy_parser.py", line 894, in parse_expr 
    return eval_expr(code, local_dict, global_dict) 
    File "/usr/local/lib/python3.5/dist-packages/sympy/parsing/sympy_parser.py", line 807, in eval_expr 
    code, global_dict, local_dict) # take local objects in preference 
    File "<string>", line 1 
    Symbol ('y')=Integer (5)*Symbol ('x')**Integer (2)-Integer (55)*Symbol ('x')**Integer (1)+Integer (140) 
       ^
SyntaxError: invalid syntax 

During handling of the above exception, another exception occurred: 

Traceback (most recent call last): 
    File "z.py", line 110, in <module> 
    solve(p, x) 
    File "/usr/local/lib/python3.5/dist-packages/sympy/solvers/solvers.py", line 833, in solve 
    f, symbols = (_sympified_list(w) for w in [f, symbols]) 
    File "/usr/local/lib/python3.5/dist-packages/sympy/solvers/solvers.py", line 833, in <genexpr> 
    f, symbols = (_sympified_list(w) for w in [f, symbols]) 
    File "/usr/local/lib/python3.5/dist-packages/sympy/solvers/solvers.py", line 824, in _sympified_list 
    return list(map(sympify, w if iterable(w) else [w])) 
    File "/usr/local/lib/python3.5/dist-packages/sympy/core/sympify.py", line 356, in sympify 
    raise SympifyError('could not parse %r' % a, exc) 
sympy.core.sympify.SympifyError: Sympify of expression 'could not parse 'y = 5*x**2 - 55*x**1 + 140'' failed, because of exception being raised: 
SyntaxError: invalid syntax (<string>, line 1) 

を、あなたは**と*として乗算記号で指数を記述する必要があります。それ以外にも、私はSympy固有の構文が本当に分かりません。

Answer 1

私は記号xとyの観点から多項式を定義する必要があると思います。 solveは、多項式がゼロに等しいと仮定しているので、以下のようにyを減算します。 Pythonの3.5.2で：

from sympy import Symbol, polys, solve 
x = Symbol('x') 
y = Symbol('y') 
for i in range(10): 
    p = polys.specialpolys.random_poly(x,2,-1000,1000) - y # equals zero 
    print("p orig " + str(p)) 

    p_solution_x = solve(p, x) 
    print('p_solution_x:', p_solution_x) 

    p_solution_y = solve(p, y) 
    print('p_solution_y:', p_solution_y) 

は、この結果を与える：

p orig -292*x**2 - 550*x - y - 984 
p_solution_x: [-sqrt(-292*y - 211703)/292 - 275/292, sqrt(-292*y - 211703)/292 - 275/292] 
p_solution_y: [-292*x**2 - 550*x - 984] 
p orig 969*x**2 + 809*x - y - 676 
p_solution_x: [-sqrt(3876*y + 3274657)/1938 - 809/1938, sqrt(3876*y + 3274657)/1938 - 809/1938] 
p_solution_y: [969*x**2 + 809*x - 676] 
p orig -604*x**2 + 382*x - y - 705 
p_solution_x: [-sqrt(-604*y - 389339)/604 + 191/604, sqrt(-604*y - 389339)/604 + 191/604] 
p_solution_y: [-604*x**2 + 382*x - 705] 
p orig -721*x**2 - 846*x - y - 908 
p_solution_x: [-sqrt(-721*y - 475739)/721 - 423/721, sqrt(-721*y - 475739)/721 - 423/721] 
p_solution_y: [-721*x**2 - 846*x - 908] 
p orig 422*x**2 + 77*x - y + 914 
p_solution_x: [-sqrt(1688*y - 1536903)/844 - 77/844, sqrt(1688*y - 1536903)/844 - 77/844] 
p_solution_y: [422*x**2 + 77*x + 914] 
p orig 847*x**2 - 273*x - y - 68 
p_solution_x: [-sqrt(3388*y + 304913)/1694 + 39/242, sqrt(3388*y + 304913)/1694 + 39/242] 
p_solution_y: [847*x**2 - 273*x - 68] 
p orig -703*x**2 + 587*x - y + 589 
p_solution_x: [-sqrt(-2812*y + 2000837)/1406 + 587/1406, sqrt(-2812*y + 2000837)/1406 + 587/1406] 
p_solution_y: [-703*x**2 + 587*x + 589] 
p orig -999*x**2 + 827*x - y + 699 
p_solution_x: [-sqrt(-3996*y + 3477133)/1998 + 827/1998, sqrt(-3996*y + 3477133)/1998 + 827/1998] 
p_solution_y: [-999*x**2 + 827*x + 699] 
p orig 364*x**2 + 517*x - y - 552 
p_solution_x: [-sqrt(1456*y + 1071001)/728 - 517/728, sqrt(1456*y + 1071001)/728 - 517/728] 
p_solution_y: [364*x**2 + 517*x - 552] 
p orig 456*x**2 - 852*x - y + 144 
p_solution_x: [-sqrt(114*y + 28953)/228 + 71/76, sqrt(114*y + 28953)/228 + 71/76] 
p_solution_y: [456*x**2 - 852*x + 144]