When working with mathematical functions in Python, it’s common to need to find the derivative of a function. This can be done using a variety of methods, including numerical differentiation and symbolic differentiation. In this article, we’ll explore both approaches and provide code examples for each.
Numerical Differentiation
Numerical differentiation is a method for approximating the derivative of a function using finite differences. The basic idea is to approximate the slope of the function at a point by computing the difference between two values of the function over a small interval. There are two main methods for numerical differentiation: forward differencing and central differencing.
Forward Differencing
The forward difference method approximates the derivative of a function at a point x0 using the formula:
f'(x0) ≈ (f(x0 + h) – f(x0))/h
where h is a small step size. This method is called forward differencing because it uses values of the function that come after x0.
Here’s an example of how to implement the forward difference method in Python:
def f(x):
return x**2
def forward_difference(f, x, h):
return (f(x+h)  f(x))/h
print(forward_difference(f, 2, 0.1)) # Returns 4.1
Central Differencing
The central difference method approximates the derivative of a function at a point x0 using the formula:
f'(x0) ≈ (f(x0 + h) – f(x0 – h))/(2h)
This method is called central differencing because it uses values of the function both before and after x0.
Here’s an example of how to implement the central difference method in Python:
def f(x):
return x**2
def central_difference(f, x, h):
return (f(x+h)  f(xh))/(2*h)
print(central_difference(f, 2, 0.1)) # Returns 4.0
Symbolic Differentiation
Symbolic differentiation is a method for finding exact expressions for the derivative of a function using mathematical symbols and rules. This approach is more accurate than numerical differentiation and can handle more complex functions. There are many symbolic differentiation packages available for Python, but we’ll focus on the builtin sympy
module.
Here’s an example of how to use sympy
to find the derivative of a simple function:
import sympy
x = sympy.Symbol('x')
f = x**2
f_prime = sympy.diff(f, x)
print(f_prime) # Returns 2*x
In this example, we define a symbolic variable x
and a function f
. We then use the sympy.diff
function to find the derivative of f
with respect to x
, which gives us the expression 2*x
. We can then substitute in a value for x
to evaluate the derivative at a specific point.
print(f_prime.subs(x, 2)) # Returns 4
Conclusion
Finding the derivative of a function in Python can be done using either numerical differentiation or symbolic differentiation. Both approaches have their pros and cons, and the best method to use depends on the specific problem at hand. Numerical differentiation is relatively simple to implement, but is less accurate and can suffer from issues with numerical stability. Symbolic differentiation is more accurate and provides exact expressions for the derivative, but can be more complex and computationally intensive. By understanding the different methods available and their tradeoffs, you can choose the approach that best fits your needs.
Numerical differentiation is a widely used method for approximating the derivative of a function, especially when an analytic solution is not readily available or impractical to compute. The forward difference and central difference methods are two common numerical differentiation techniques. The forward difference method uses values of the function that come after the point of interest, while the central difference method uses values before and after the point of interest. The choice of method depends on the problem at hand and the required accuracy of the solution.
In the example code for the forward difference method, the forward_difference
function takes as input a function f
, an evaluation point x
, and a step size h
. The function computes the value of the function at x+h
and x
, and then calculates their difference, which is then divided by h
. In the example, f(x) = x**2
, and the evaluation point is x=2
. The step size is set to 0.1
, and the function returns the approximate value of the derivative of f
at x=2
. The output is 4.1
, which is an approximation of the true value of f'(2)
.
The central difference method is similar to the forward difference method, but it uses values of the function both before and after the point of interest. In the example code, the central_difference
function takes as input a function f
, an evaluation point x
, and a step size h
. The function computes the value of the function at x+h
and xh
, and then calculates their difference, which is then divided by 2h
. In this example, f(x)=x**2
, and the evaluation point is x=2
. The step size is set to 0.1
, and the function returns the approximate value of the derivative of f
at x=2
. The output is 4.0
, which is an approximation of the true value of f'(2)
.
Symbolic differentiation is a powerful method for finding exact expressions for the derivative of a function. The sympy
module provides an easytouse interface for symbolic differentiation in Python. The example code shows how to find the derivative of the function f(x)=x**2
using sympy
by defining a symbolic variable x
, defining the function f
, and then using the diff
function to compute the derivative of f
with respect to x
. The function returns 2*x
, which is the exact symbolic expression for the derivative of f
.
The subs
function is then used to substitute a value for x
in the derivative expression to evaluate the derivative at a specific point. In this example, x
is substituted with the value 2
, which returns the output 4
, which is the exact value of the derivative of f
at x=2
. Symbolic differentiation is a powerful tool, especially for solving complex problems that numerical methods may struggle to handle.
In conclusion, numerical differentiation and symbolic differentiation are two powerful methods to find the derivative of a function in Python. When choosing a method, it's important to consider the problem at hand and the required accuracy of the solution. Numerical differentiation is relatively simple to implement, but may suffer from numerical instability, while symbolic differentiation can handle more complex problems but may be more computationally intensive.
Popular questions

What is numerical differentiation?
Numerical differentiation is a method of approximating the derivative of a function using finite differences. The basic idea is to approximate the slope of the function at a point by computing the difference between two values of the function over a small interval. 
What is symbolic differentiation?
Symbolic differentiation is a method of finding the exact expressions for the derivative of a function using mathematical symbols and rules. 
What is the difference between forward differencing and central differencing?
Forward differencing uses values of the function that come after the point of interest, while central differencing uses values before and after the point of interest. 
What is the purpose of the
sympy
module in finding the derivative of a function?
Thesympy
module provides an easytouse interface for symbolic differentiation in Python. It can be used to find exact expressions for the derivative of a function, which is useful for solving complex problems. 
Which method is more accurate: numerical or symbolic differentiation?
Symbolic differentiation is generally more accurate than numerical differentiation, as it provides exact expressions for the derivative. Numerical differentiation can suffer from numerical instability and errors caused by the choice of step size.
Tag
Derivatives