CODEWITHSUNDEEP
pythonsympy
Ayush Aggarwal
Ayush Aggarwal

Reputation: 23

"PolynomialError: only univariate polynomials are allowed" when solving a system of inequalities

I want to find the interval of following two constants cons1 and cons2 I wrote the follwing code 

 from sympy import Poly
 from sympy import Abs
 from sympy.solvers.inequalities import solve_rational_inequalities
 from sympy.abc import x
 cons1=2*((x+2)**2)-Abs(x)-1
 cons2=exp(2*x+1)-2.5
 solve_rational_inequalities([[((Poly(cons1), Poly(1, x)), '<='), (Poly(cons2), Poly(1, x)), '<=')]])

but because of Abs I am getting:

PolynomialError: only univariate polynomials are allowed

Upvotes: 2

Views: 696

Answers (1)

user6655984
user6655984

Reputation:

This is by design. 2*((x+2)**2) - Abs(x) - 1 is not a polynomial in x. Neither is exp(2*x+1) - 2.5. The methods of solve_rational_inequalities do not apply to such functions.

If you try to cheat mathematics by wrapping those expressions in Poly, all that happens is that SymPy will make them polynomials with respect to x and Abs(x) (or exp(2*x+1), etc). That's a kind of a polynomial, but not a polynomial with respect to x, which is what solve_rational_inequalities requires. Hence the error.

Bottom line: SymPy does not currently have an algorithm for solving systems of general inequalities. There is an algorithm for rational inequalities and some other things listed on inequality solvers page, including solve_univariate_inequality (which allows general functions, but for one variable only).

Upvotes: 2

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