pylab draw tangent lines

pylab_draw_tangent_line.py

import numpy as np
import pylab

class MathDraw():
    def __init__(self, func):
        self.f = func
        self.vf = np.vectorize(func)

    def draw(self, x_start=-5.0, y_end=5.0):
        x = np.arange(x_start, y_end, 0.1)
        y = self.vf(x)
        pylab.plot(x, y, 'b')
    
    def draw_tangent(self, *args, length=1, color='--r'):
        f = self.f
        xlist = args
        for x in xlist:
            unit = 0.1
            length = length / 2
            tangent_x = np.arange(x-length, x+length+unit, unit)

            h = 0.1 # the micro difference in x
            f_prime = (f(x+h) - f(x)) / h # derivative
            tangent_y = f_prime * (tangent_x - x) + f(x) # tangent

            # plot of the point and the tangent
            pylab.plot(x, f(x), 'om', tangent_x, tangent_y, color)

    def show(self):
        pylab.show()


def func(x): # sample function
    return x*np.sin(np.power(x,2))

m = MathDraw(func)
m.draw(-2, 4)
m.draw_tangent(-1.5, 1.5, 2.15, length=2)
m.show()