How can i solve this inequality in python? RecursionError: maximum recursion depth exceeded while getting the str of an object

Question

I am trying to get the interval of acceptable values in this inequality:

12/300 < 0.45*sympy.sqrt(Ro/(2*f*x))

where R is calculated in the code.

I want the interval of x. How can I get it?

#Introduzindo as variaveis
P = 50
Vin = 300
Vout = 12
f = 50000
DVout = 0.05
D = 0.45
Ts = 1/f

#Programa
import numpy as np
import sympy
from sympy import *

Ro = Vout**2/P
a = Vout/Vin

x = Symbol('x')
q = solve_univariate_inequality(a <= D*sympy.sqrt(Ro/(2*f*x)), x, S.Reals)

Error:

RecursionError                            Traceback (most recent call last)
<ipython-input-53-6eeaca6392d4> in <module>
     19 # # var('x')
     20 x = Symbol('x')
---> 21 q = solve_univariate_inequality(a <= D*sympy.sqrt(Ro/(2*f*x)), x, S.Reals)
     22 # solvify(D*sympy.sqrt(Ro/(2*f*x)), x, S.Reals)
     23 # # solvify(D*sympy.sqrt(Ro/(2*f*x), x))

12 frames
... last 9 frames repeated, from the frame below ...

/usr/local/lib/python3.7/dist-packages/sympy/solvers/solveset.py in _solveset(f, symbol, domain, _check)
   1060                         result += _solve_radical(equation,
   1061                                                  symbol,
-> 1062                                                  solver)
   1063                     elif equation.has(Abs):
   1064                         result += _solve_abs(f, symbol, domain)

RecursionError: maximum recursion depth exceeded while getting the str of an object

a <= D... is not how you express an inequality in sympy. Reread the sympy docs about 'relationals'. — hpaulj
– hpaulj, Commented Sep 13, 2022 at 22:20

Oscar Benjamin · Accepted Answer · 2022-09-13 22:30:19Z

1

What version of SymPy are you using? I tried with the current version (1.11) and I got:

In [1]: #Introduzindo as variaveis
   ...: P = 50
   ...: Vin = 300
   ...: Vout = 12
   ...: f = 50000
   ...: DVout = 0.05
   ...: D = 0.45
   ...: Ts = 1/f
   ...: 
   ...: #Programa
   ...: import numpy as np
   ...: import sympy
   ...: from sympy import *
   ...: 
   ...: Ro = Vout**2/P
   ...: a = Vout/Vin
   ...: 
   ...: x = Symbol('x')
   ...: q = solve_univariate_inequality(a <= D*sympy.sqrt(Ro/(2*f*x)), x, S.Reals)

In [2]: q
Out[2]: x ≤ 0.003645 ∧ 0 < x

answered Sep 13, 2022 at 22:30

Oscar Benjamin

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3 Comments

Karl Knechtel Over a year ago

If the error is not reproducible, then there is not a question. Please read How to Answer and do not use the answer section to say "I tried your code and got a different result". If you changed something, explain what you changed and why. Otherwise, do not answer off-topic questions (the definition here includes questions about problems that cannot be reproduced). I can see that you are not at all new to answering questions on Stack Overflow; I shouldn't need to remind you of this.

hpaulj Over a year ago

@KarlKnechtel, Oscar is one of the top sympy posters here. Let him judge what is a good answer.

Oscar Benjamin Over a year ago

The point is that the OP is probably using an older SymPy version and should consider upgrading. Checking now I can reproduce their problem with SymPy 1.7 but as shown here it is fixed in newer versions. It's not "I tried your code and got a different result" but rather "I tried your code with the latest version and got a different result".

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