# Finding the phase of a transfer function symbolically in python

When working with transfer functions in control systems, it is often necessary to find the phase of the transfer function symbolically. In Python, there are several ways to accomplish this task. In this article, we will explore three different approaches to solve this problem.

## Approach 1: Using the Sympy Library

The Sympy library is a powerful tool for symbolic mathematics in Python. To find the phase of a transfer function symbolically, we can use the Sympy library’s built-in functions.

``````import sympy as sp

# Define the transfer function symbolically
s = sp.symbols('s')
G = (s + 1) / (s**2 + 2*s + 1)

# Find the phase of the transfer function
phase = sp.atan2(sp.im(G), sp.re(G))

# Print the phase
print(phase)``````

This approach uses the atan2 function from the Sympy library to calculate the phase of the transfer function. The atan2 function takes the imaginary and real parts of the transfer function as arguments and returns the phase in radians.

## Approach 2: Using the Numpy Library

The Numpy library is another popular library for numerical computing in Python. Although it is primarily designed for numerical calculations, it can also be used to find the phase of a transfer function symbolically.

``````import numpy as np

# Define the transfer function symbolically
s = np.complex128('s')
G = (s + 1) / (s**2 + 2*s + 1)

# Find the phase of the transfer function
phase = np.angle(G)

# Print the phase
print(phase)``````

This approach uses the angle function from the Numpy library to calculate the phase of the transfer function. The angle function takes the complex transfer function as an argument and returns the phase in radians.

## Approach 3: Using the Control Library

The Control library is a Python library specifically designed for control systems engineering. It provides a wide range of functions for analyzing and designing control systems. To find the phase of a transfer function symbolically, we can use the Control library’s built-in functions.

``````import control

# Define the transfer function symbolically
s = control.TransferFunction.s
G = (s + 1) / (s**2 + 2*s + 1)

# Find the phase of the transfer function
phase = control.phase(G)

# Print the phase
print(phase)``````

This approach uses the phase function from the Control library to calculate the phase of the transfer function. The phase function takes the transfer function as an argument and returns the phase in degrees.

After exploring these three approaches, it is clear that the best option depends on the specific requirements of the problem. If symbolic calculations are required, the Sympy library is the most suitable choice. If numerical calculations are sufficient, both the Numpy and Control libraries can be used. However, the Control library provides additional functionality specifically tailored for control systems engineering, making it a preferred choice in that domain.

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### 3 Responses

1. Alonso Sheppard says:

Approach 3 is the way to go! Control library FTW 🙌🔥

2. Nikolai Elliott says:

Approach 3 seems to be the winner, but can we really trust those control freaks? 🤔

3. Makenzie Huerta says:

Approach 1 seems simple and straightforward, but can Approach 3 handle more complex transfer functions? 🤔