TypeError for derivative function

Question

I used sympy to find derivative of a function.

( )= −5+√(4− ^2)

import sympy
def f_derivative(x):
  x = sympy.Symbol('x')
  f = x - 5 + (4 - x**2)**0.5
  derivative_f = f.diff(x)
  derivative_f = sympy.lambdify(x, derivative_f)
  print(derivative_f(1))
f_derivative(1)
assert f_derivative(1) - 0.42264973 < 1e-5

However, there is an error when I use assert to check

TypeError: unsupported operand type(s) for -: ‘NoneType’ and ‘float’

Please let me know how to fix it

Asked By: Phung Doan

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Source

Answer 1

Here is an updated version of the code that should work as expected:

import sympy

def f_derivative(x):
  f = x - 5 + (4 - x**2)**0.5
  derivative_f = f.diff(x)
  derivative_f = sympy.lambdify(x, derivative_f)
  return derivative_f(x)

assert abs(f_derivative(1) - 0.42264973) < 1e-5

Answered By: Haris

Answer 2

import sympy
def f_derivative(x):
  x = sympy.Symbol('x')
  f = x - 5 + (4 - x**2)**0.5
  derivative_f = f.diff(x)
  derivative_f = sympy.lambdify(x, derivative_f)
  result = derivative_f(1)
  assert result - 0.42264973 < 1e-5
  print(result)
f_derivative(1)

I hope helped you

Answered By: Lucas Fernandes

TypeError for derivative function

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