CODEWITHSUNDEEP
pythonvectormatplotlib
pceccon
pceccon

Reputation: 9844

Change axes ticks of quiver - Python

I'm plotting a vector field with the quiver method of Matplotlib.

My array to store this vector has a dimension x * y but I'm working with a space that varies from -2 to 2.

So far, to plot the vector field I have this method:

import matplotlib.pyplot as plt

def plot_quiver(vector_field_x, vector_field_y, file_path):
    plt.figure()
    plt.subplots()
    plt.quiver(vector_field_x, vector_field_y)
    plt.savefig(file_path + '.png')
    plt.close()

Which gives me this output, as an example, for a 10 x 10 array:

enter image description here

But to generate this vector field I centered my data in the x = 0, y = 0, x and y ranging from -2 to 2. Then, I would like to plot the axis of the image following this pattern.

As an standard approach, I tried to do the following:

def plot_quiver(vector_field_x, vector_field_y, file_path):
    plt.figure()
    fig, ax = plt.subplots()
    ax.quiver(vector_field_x, vector_field_y)
    ax.set_xticks([-2, 0, 2])
    ax.set_yticks([-2, 0, 2])    
    plt.savefig(file_path + '.png')
    plt.close()

Which usually works with Matplotlib methods, as imshow and streamplot, for example.

But this what I've got with this code:

enter image description here

Which is not what I want.

So, I'm wondering how can I perform what I explained here to change the axes ticks.

Thank you in advance.

Upvotes: 1

Views: 1455

Answers (1)

mgab
mgab

Reputation: 3964

Funny thing, I just learnt about quiver yesterday... :)

According to the quiver documentation, the function can accept from 2 to 5 arguments...

The simplest way to use the function is to pass it two arrays with equal number of elements U and V. Then, matplotlib will plot an arrow for each element in the arrays. Specifically, for each element i,j you will get an arrow placed at i,j and with components defined by U[i,j] and V[i,j]. This is what is happening to you

A more complete syntax is to pass our arrays with equal number of elements X, Y, U and V. Again, you will get an arrow for each i,j element with components defined by U[i,j] and V[i,j], but this time they will be placed at coordinates X[i,j], Y[i,j].

In conclusion:

you need to call quiver like

quiver(values_x, values_y, vector_field_x, vector_field_y)

Probably you already did it, but you can get values_x and values_y using the numpy.meshgrid function.

The matplotlib example for the quiver function might be useful, also.

I hope it helps!

Upvotes: 1

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