# Python - Matplotlib

Table of Content

### Preface

Goal: Plot a Chart based on Math Equation.

I also wish that I had matplotlib, while I was studying Engineering Degree. My final assignment was data acquisition, Realtime data taken from diesel engine, and the representation of P-V diagram, should be shown immediately on desktop screen.

I think matplotlib should be just the right tool for that kind of chart. Now that I meet Data Science, and Functional Programming, I also have a need to plot down chart, in a blog, or sent chart via Telegram or Whatsapp using PNG image

Despite of my regret, I try to make myself a basic script, to show equation in matplotlib.

### 2D Line

The python script is simple

import numpy as np
import matplotlib
matplotlib.rcParams['text.usetex'] = True
import matplotlib.pyplot as plt

def f(x):
return x**2 - 12*x - 64

x    = np.arange(-6, 16, 0.2)
xdot = np.arange(-6, 16, 1)

plt.plot(x, f(x), 'k', xdot, f(xdot), 'bo')
plt.axis([-10, 20, -120, 60])

plt.axhline(y=0, color='k')
plt.axvline(x=0, color='k')

plt.grid()
plt.title(r'$y = x^2 - 12x - 64$', fontsize=16, color='b', y=1.04)
plt.xlabel('Just X')
plt.ylabel('Just Y')

plt.show()

Then run the folowing command

$python yourscript.py This will show you this below: ### 3D Surface The python script is a little bit longer. # This import registers the 3D projection, but is otherwise unused. from mpl_toolkits.mplot3d import Axes3D import matplotlib matplotlib.rcParams['text.usetex'] = True import matplotlib.pyplot as plt from matplotlib import cm from matplotlib.ticker import LinearLocator, FormatStrFormatter import numpy as np def f(x, y): return x**2 + y**2 - 12*x + 12*y + x*y - 64 # plot figure fig = plt.figure() ax = fig.gca(projection='3d') # Make data. X = np.arange(-5, 5.1, 0.2) Y = np.arange(-5, 5.1, 0.2) X, Y = np.meshgrid(X, Y) Xline = np.arange(-5, 5.1, 1) Yline = np.arange(-5, 5.1, 1) Xline, Yline = np.meshgrid(Xline, Yline) # Compute z to make the surface. Z = f(X, Y) Zline = f(Xline, Yline) # Plot the surface. surf = ax.plot_surface(X, Y, Z, cmap=cm.viridis, linewidth=1, antialiased=False) wire = ax.plot_wireframe(Xline, Yline, Zline) # Customize the z axis. ax.set_zlim(-151, 76) ax.zaxis.set_major_locator(LinearLocator(10)) ax.zaxis.set_major_formatter(FormatStrFormatter('%.02f')) # Add a color bar which maps values to colors. fig.colorbar(surf, shrink=0.5, aspect=5) # Make a 3D quiver plot x, y, z = np.zeros((3,3)) u, v, w = np.array([[1,1,0],[1,0,1],[0,1,1]]) ax.quiver(x,y,z,u,v,w,arrow_length_ratio=0.1) # Some decoration plt.suptitle('Easy Quadratic Chart') plt.xlabel('Just X') plt.ylabel('Just Y') ax.set_zlabel('Just Z', rotation=90) # set z ticks ax.set_zticks(np.arange(-150, 50, 25)) # latex plt.title(r'$z = x^2 + y^2 - 12x + 12y + xy - 64\$',
fontsize=16, color='b', y=1.06)

# finally
plt.show()

This will show you this below:

That is all. I keep these two scripts in my blog, so I can find any of them easily later. Plotting with matplotlib is fun.

What do you think ?