Method to return the equation of a straight line given two points

Question

I have a class Point, consisting of a point with x and y coordinates, and I have to write a method that computes and returns the equation of a straight line joi

Answer 1

Let's assume that we have the following points:

P0: ( x0 = 100, y0 = 240 )

P1: ( x1 = 400, y1 = 265 )

We can compute the coefficients of the line y = a*x + b that connects the two points using the polyfit method from numpy.

import numpy as np
import matplotlib.pyplot as plt

# Define the known points
x = [100, 400]
y = [240, 265]

# Calculate the coefficients. This line answers the initial question. 
coefficients = np.polyfit(x, y, 1)

# Print the findings
print 'a =', coefficients[0]
print 'b =', coefficients[1]

# Let's compute the values of the line...
polynomial = np.poly1d(coefficients)
x_axis = np.linspace(0,500,100)
y_axis = polynomial(x_axis)

# ...and plot the points and the line
plt.plot(x_axis, y_axis)
plt.plot( x[0], y[0], 'go' )
plt.plot( x[1], y[1], 'go' )
plt.grid('on')
plt.show()

a = 0.0833333333333

b = 231.666666667

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For installing numpy: http://docs.scipy.org/doc/numpy/user/install.html