Plot two vectors in python

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[]

user

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asked Feb 16, 2017 at 18:30

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

DSH

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answered Feb 16, 2017 at 20:31

Aziz AltoAziz Alto

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7

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[]

answered Feb 16, 2017 at 19:44

fugledefuglede

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Your main problem is you create new figures in your loop, so each vector gets drawn on a different figure. Here's what I came up with, let me know if it's still not what you expect:

CODE:

import numpy as np
import matplotlib.pyplot as plt
M = np.array[[[1,1],[-2,2],[4,-7]]]

rows,cols = M.T.shape

#Get absolute maxes for axis ranges to center origin
#This is optional
maxes = 1.1*np.amax[abs[M], axis = 0]

for i,l in enumerate[range[0,cols]]:
    xs = [0,M[i,0]]
    ys = [0,M[i,1]]
    plt.plot[xs,ys]

plt.plot[0,0,'ok'] #