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pythonmatplotlibmathgraphing

Graph parabola in matplotlib with vertex and 2 'end' points known

Trying to create a parabolic vector of values where the Vertex and two other points along the parabola are known.

Example...

  • Range from 0 to 10
  • Vertex = [5,2]
  • Coordinate 1 = [1,1]
  • Coordinate 2= [10,1]

Example Desired result

Any help/advice is greatly appreciated.

Thanks

Solution

  • I would use numpy to adjust a parabola passing by the points with polyfit, and then polyval to evaluate the polynomial found:

    import matplotlib.pyplot as plt
import numpy as np

#points
x = [1, 5, 10]
y = [1, 2, 1]

poly_coeffs = np.polyfit(x,y,2) #fit a polynomial with degree=2

#evaluation points vector xx
xmin = 0
xmax = 10
xx = np.linspace(xmin, xmax, 100)
yy = np.polyval(poly_coeffs, xx) #y coords

#ploting
plt.figure()
plt.plot(x,y,'or')
plt.plot(xx,yy)
plt.grid()
plt.ylim([-3,4])
plt.xlim([-0.5,12])

    This would draw the next image: