How to plot vectors in python using matplotlib

Question

I am taking a course on linear algebra and I want to visualize the vectors in action, such as vector addition, normal vector, so on.

For instance:

V = np.array([[1,1],[-2,2],[4,-7]]) 

In this case I want to plot 3 vectors V1 = (1,1), M2 = (-2,2), M3 = (4,-7).

Then I should be able to add V1,V2 to plot a new vector V12(all together in one figure).

when I use the following code, the plot is not as intended

import numpy as np import matplotlib.pyplot as plt M = np.array([[1,1],[-2,2],[4,-7]])  print("vector:1") print(M[0,:]) # print("vector:2") # print(M[1,:]) rows,cols = M.T.shape print(cols)  for i,l in enumerate(range(0,cols)):     print("Iteration: {}-{}".format(i,l))     print("vector:{}".format(i))     print(M[i,:])     v1 = [0,0],[M[i,0],M[i,1]]     # v1 = [M[i,0]],[M[i,1]]     print(v1)     plt.figure(i)     plt.plot(v1)     plt.show() 

Answer 1

How about something like

import numpy as np import matplotlib.pyplot as plt  V = np.array([[1,1], [-2,2], [4,-7]]) origin = np.array([[0, 0, 0],[0, 0, 0]]) # origin point  plt.quiver(*origin, V[:,0], V[:,1], color=['r','b','g'], scale=21) plt.show() 

Then to add up any two vectors and plot them to the same figure, do so before you call plt.show(). Something like:

plt.quiver(*origin, V[:,0], V[:,1], color=['r','b','g'], scale=21) v12 = V[0] + V[1] # adding up the 1st (red) and 2nd (blue) vectors plt.quiver(*origin, v12[0], v12[1]) plt.show() 

NOTE: in Python2 use origin[0], origin[1] instead of *origin

Answer 2

This may also be achieved using matplotlib.pyplot.quiver, as noted in the linked answer;

plt.quiver([0, 0, 0], [0, 0, 0], [1, -2, 4], [1, 2, -7], angles='xy', scale_units='xy', scale=1) plt.xlim(-10, 10) plt.ylim(-10, 10) plt.show()