Time for action – plotting a polynomial and its derivatives

Let's plot a polynomial and its first and second derivative. We will make three subplots for the sake of clarity:

  1. Create a polynomial and its derivatives using the following code:
    func = np.poly1d(np.array([1, 2, 3, 4]).astype(float))
x = np.linspace(-10, 10, 30)
y = func(x)
func1 = func.deriv(m=1)
y1 = func1(x)
func2 = func.deriv(m=2)
y2 = func2(x)
  2. Create the first subplot of the polynomial with the subplot() function. The first parameter of this function is the number of rows, the second parameter is the number of columns, and the third parameter is an index number starting with 1. Alternatively, combine the three parameters into a single number, such as 311. The subplots will be organized in three rows and one column. Give the subplot the title Polynomial. Make a solid red line:
    plt.subplot(311)
plt.plot(x, y, 'r-')
plt.title("Polynomial")
  3. Create the third subplot of the first derivative with the subplot() function. Give the subplot the title First Derivative. Use a line of blue triangles:
    plt.subplot(312)
plt.plot(x, y1, 'b^')
plt.title("First Derivative")
  4. Create the second subplot of the second derivative with the subplot() function. Give the subplot the title Second Derivative. Use a line of green circles:
    plt.subplot(313)
plt.plot(x, y2, 'go')
plt.title("Second Derivative")
plt.xlabel('x')
plt.ylabel('y')
plt.show()

    The three subplots with polynomial coefficients 1, 2, 3, and 4 are as follows:

    Time for action – plotting a polynomial and its derivatives

What just happened?

We plotted a polynomial and its first and second derivatives using three different line styles and three subplots in three rows and one column (see polyplot3.py):

import numpy as np
import matplotlib.pyplot as plt

func = np.poly1d(np.array([1, 2, 3, 4]).astype(float))
x = np.linspace(-10, 10, 30)
y = func(x)
func1 = func.deriv(m=1)
y1 = func1(x)
func2 = func.deriv(m=2)
y2 = func2(x)

plt.subplot(311)
plt.plot(x, y, 'r-')
plt.title("Polynomial")
plt.subplot(312)
plt.plot(x, y1, 'b^')
plt.title("First Derivative")
plt.subplot(313)
plt.plot(x, y2, 'go')
plt.title("Second Derivative")
plt.xlabel('x')
plt.ylabel('y')
plt.show()
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