import numpy as np
import matplotlib.pyplot as plt
from scipy.special import erf

x=np.arange(-5,5,0.01)
plt.plot(x,erf(x))
plt.xlim(-5,5)
plt.xlabel('x')
plt.ylabel('erf(x)')
plt.show()

erf(-1/np.sqrt(2))

-0.6826894921370859