CODEWITHSUNDEEP
pythonsympy
Quinten Rosseel
Quinten Rosseel

Reputation: 25

How to pass (custom) functions to the "locals" argument of simpify?

I have two functions, sqrt(x) and pow(x, y), that I want to pass to the "local" argument of sympify upon receiving "sqrt(pow(x,2))" as a string. After this, the goal is to simplify the expression from "sqrt(pow(x,2))" to "x" using simplify.

The code below outputs 'sqrt(x**2)', giving me a hint that the pow(x, y) function is picked up, but not further simplified for an unknown reason. 

import sympy as sp

# Function Definitions
def pow(x, y):
   return x ** y

def sqrt(x):
   return sp.sqrt(x)

sp.symbols('x', positive=True, real=True)
input_exp = 'sqrt(pow(x, 2))'

eqn = sp.sympify(input_exp, locals={'sqrt': sqrt, 'pow': pow})
print("Simplification: ", sp.simplify(eqn))

The code below correctly outputs an 'x', but has a sympy expression as input. For my usecase, this needs to be a string. Replacing this sympy expression with a call to sp.sympify(input_exp, locals={'sqrt': sqrt, 'pow': pow}) does not work either. 

import sympy as sp
from sympy import Function

# Function definitions
class pow(Function):
   @classmethod
   def eval(cls, x, y):
      return x ** y


class sqrt(Function):
   @classmethod
   def eval(cls, x):
      return sp.sqrt(x)


# Simplify the expression.
x = sp.symbols('x', positive=True, real=True)
print("Simplification: ", sp.simplify(sqrt(pow(x, 2))))

Any suggestion or solutions are more then welcome. Thank you!

Upvotes: 2

Views: 642

Answers (1)

Omi
Omi

Reputation: 121

You need to pass 'x' as well as a local reference. Here is the code :

import sympy as sp

# Function Definitions
def pow(x, y):
   return x ** y

def sqrt(x):
   return sp.sqrt(x)

x = sp.symbols('x', positive=True, real=True)
input_exp = 'sqrt(pow(x, 2))'


eqn = sp.sympify(input_exp, locals={'sqrt': sqrt, 'pow': pow, 'x':x})
print("Simplification: ", sp.simplify(eqn))

and 

import sympy as sp
from sympy import Function

# Function definitions
class pow(Function):
   @classmethod
   def eval(cls, x, y):
      return x ** y


class sqrt(Function):
   @classmethod
   def eval(cls, x):
      return sp.sqrt(x)


# Simplify the expression.
x = sp.symbols('x', positive=True, real=True)
input_exp = 'sqrt(pow(x, 2))'
eqn = sp.sympify(input_exp, locals={'sqrt': sqrt, 'pow': pow, 'x':x})
print("Simplification: ", sp.simplify(eqn))

Upvotes: 2

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